As some of you might know World of Goo doesn't have DRM and as a result, people will ofcourse buy the game to show their appreciation to the dev team, since they won't be bothered by an obtrusive anti-piracy tool... right?
.... apparantly not. One of the devs estimates that up to 90% of the PC-version are pirated copies.
I'm absolutely flabbergasted! It's a great game, no DRM, it's only 20$ and still 9 out of 10 choose to pirate the game. I guess no DRM is only a good idea on older games.

I would very much like to know how did he estimate that.
Wrong. Games with built-in DRM are pirated more often, because apart from your usual pirate, they are copied illegaly by people who would've bought it (if not for DRM), and by people who indeed bought it, but are not willing to install it from the original media, with all the malware included. Let's be honest - DRM has NEVER stopped anyone from illegally downloading a game.

I am unsure if sahib's theory is correct, but I am very sure that especially in the case of World of Goo DRM or no DRM wouldn't have made any difference. For the "hackers" it doesn't even seem to be a great problem or a very time-consuming task to crack even the strongest copy protections, but especially for games with more typical copy protections, like I suppose World of Goo would have been, it seems to be nothing but a routine to them.
So, while it is indeed sad to see how World of Goo got pirated instantly and massively, I think it's still better that 2Dboy didn't use any DRM.
Put very simply: DRM: Pirates don't care, honest buyers get annoyed. No DRM: Pirates still don't care, honest buyers are pleased.
[edit]
Oh, in the article about this on 2Dboy.com the developers actually drew a similiar conclusion when comparing their DRM-free World of Goo to the DRM-protected Ricochet Infinity:

I'm not particularly interested in the game, and I figure with a title like World Of Goo, where it's virtually unknown whether or not it would be a good game, people aren't willing to jump into a new title and pay for it. It's sad really, you have to have a block buster hit in order to be able to sell your game w/o drm. But I was also going to say, that there have been a number of times where I told someone about GOG.com and to get fallout and they say 'Oh, I just pirate it, I pirate everything.' and given my line of work, where we deal with people who share copyrighted material on a daily basis, you'd think they'd know better, right?
It truly is a sad thing. I'll say 'Oh hey, check out GOG.com, cheap games.' and they say "I just pirate stuff." and of course I'll go "dude, it's six dollars, it's verified to work with XP and Vista, plus you get the soundtracks. If anything, consider it a six dollar soundtrack!" at that point though, I've lost them.

That really is unfortunate. Some people are just going to pirate no matter how cheap it is or how well supported it is. You could always just smack them upside the head like I did with my co-worker when he said he'd pirated Sins of a Solar Empire... He actually went and bought it the next day. Sometimes violence is the answer :)
I don't know if the 90% figure is accurate. They describe their system of calculating those statistics and it seems like a flawed algorthim that depends on too many uncertainties. I wouldn't be surprised to hear a number like 70 or 75%. And that's still ridiculously high.
Regardless, a $20 game with no DRM is being pirated left and right. That's really disgusting. I write software for a living, and I write game dev. related software in my spare time (and I give it away for free because I want to) and I know how much time and energy goes into development of a product. If I saw people using my crap without paying for it I'd be filled with rage too (not install-DRM mad though, I'm angry, not crazy). Hopefully some people realize after reading that article that pirates are not heroes fighting to bring down "the man". They're just assholes who happen to hate DRM as well.

Well, look at it this way: for every guy who'd pay 20$ to play the game, there are nine times as many who'd play it if it were free (and with copying software being not much of a hassle, with or without DRM, they actually do). Not much of a surprise here. The main point, that the opening post missed is that World of Goo's piracy rates are pretty much the same as that of DRM'd titles.
Also, 20$ is comparatively high for the value the game offers, just consider the stuff you can buy for 5/10$ on GOG or Steam or wherever, including various old classics. (Well, it's not like most high-profile, new releases are worth their 50$, either.) For me, it boiled down to a pretty simple question: do I want to see more inventive, nicely polished, DRM-free games from these guys? I answered 'yes' to that, and if it takes 20$ bucks to keep those guys in business, then so be it. I'm not sure how many pirates would come to the same conclusion, though. As pointed out before, it's likely they simply don't care.

Hey, I did my part, and bought my copy off WiiWare.
1500 Wii points...a small price to pay for such a gem.

I second that.
If I was a developer I would seriously consider commercials in my game. That way they would get the amount of money they deserve and piracy would cease to exist. I downloaded Prince of Persia with commercials once for free and the amount of commercials were absolutely tolerable. Such a solution would be great imo.

That excuse doesn't work when the freely available demo contains the whole of level 1.

It kind of does. A demo doesn't tell you how long a game is, for instance. Still, I didn't pirate WoG before buying it. I downloaded the demo from Steam, played it through, and went straight to the website and bought the game.
But not all games release playable demos. I wasn't talking about piracy of WoG specifically, just piracy in general.

i think some of us are missing the point of wishbones post -- that there's no way to prove that those who have pirated the game would have bought the game in the first place if a pirated version were not freely available.
and i agree with syrion -- DRM or not, games are pirated at virtually the same rate. insomniac reported that call of duty 4: modern warfare was pirated at a 90%+ rate, and that game came with some heavy DRM.
if anything, these data only support the conclusion that DRM only serves the purpose of inconveniencing honest users. like what brad wardell says, developers need to answer this question: is the purpose of DRM to increase revenues, or simply to prevent people from playing a game they would have never bought in the first place?
it's questionable whether or not DRM schemes increase sales at all, considering the success of DRM-free games and the fact that DRM-laden games are pirated at the same rate as DRM-free games.

Uhhh...CoD4 used Safedisc as it's DRM...it didn't install anything on your system. CoD5 is the same, actually.
I do agree with the base point, though. Every game gets massively pirated. This just stands out because it's not some massive gaming conglomerate, it's just a couple of guys who built a game.

Exactly. As well as the fact that some of those who did pirate it, may very well also have bought it. Some of them because they pirated it, rather than in spite of it.

The only thing I am really wondering about is how many people with a very minimal knowledge of more advanced "PC-stuff" pirate games. Those people are basically the only ones I could think of who might be discouraged from illegally downloading games by "heavier" DRM. Reading comments in P2P networks you can see that seemingly many of those guys downloading games have great trouble with even very simple problems and downloading them using a seperate application is the most advanced thing they can do. So, even when stronger copy protections get hacked quickly, it might still take some more knowledge from the user to bypass it, and therefore those "newbies" might just not be able to do it. I know at least one guy whose principle basically is "If I can get that game for free easily I'll just go for it. Who cares, it's free, so that's cool!" but who also doesn't seem to mind buying the game - if he has to.
But anyway, I guess even if this group of "pirates" is noteworthy, that alone is still not nearly reason enough for the use of those damn annoying copy protections. And maybe those people are just the "1 in 1000" mentioned in the 2Dboy.com-article.