Interesting, I will always be amused at how drm protections are put in that are often cracked before the game is even on the shelves and end up hurting nobody but people who legibly bought the game.
Legitly... Typing from my iPhone :)

Is it possible that excanging the exe caused the game settings to reset (to lower settings)?
Out of curiosity I tried it the other way round and didn't notice any drop in my framerate.

The time the game takes to start means nothing. It depends on your hard drive speed, the fragmentation of the respective volume, the fragmentation of the individual files, services running in the background, av scanners and even the actual physical location of the files on the disc. Copying a new file over an old one might change some of these properties.

I saw the same effect too, but it was only a 2-5 frame increase

I got the steam and gog versions I can't say I noticed any difference in FPS but I do have a 3.8ghz quad core.

performance is the same here with both versions. from what i read, in most cases the performance gain appears on dual core systems, or in general on lower end systems. i'm running the game on an i2500k@4,3 ghz with an oc'ed gtx460. i didn't measure the cpu-load yet, but the relatively ok temperatures suggest, that the cpu can handle the game including drm just fine (i know, this is just guessing...) so the drm seems to generate unnecessary additional cpu-load (hypothetically). don't know, if this is even possible (?)
theres a post from an cdpr-guy on the the official site (in the comments to the news somewhere) where he describes, that the publisher forced the drm on them very late in the development and that they hired an external company to implement it. so the whole thing was rushed. not an ideal situation and possibly the cause for these symptoms.

only thing i see here is the already mentioned reduced boot time without drm (4-5 sec vs. 30 or so).

Steam does not have any DRM other then Steam it self, so you wouldn't notice a difference since Steam has not been known to cause performance issues anyways.

Doesn't that depend on the laws present where the poster lives?

If anyone has purchased a retail copy and cannot use it due to DRM that was only disclosed at the last minute (so not mentioned by most stores - see Amazon.co.uk for one example) then it would take a rather perverse morality to tell them they should just suck it, especially when refunds are not generally available on software. It does mean something when it takes an extraordinarily long time (40 seconds in my case) and you have periodic CTDs requring restarts. I'm running Witcher 2 from a RAID-0 SSD (550MB/s read speed) with minimal services and no AV. I am using a crack (necessary to access the retail copy on my offline system) but given the experience of other retail users here, doubt that it's making much of a difference.

Many steam games have DRM. Steam does not remove DRM from their games. If the game included DRM originally it usually continues to have DRM even in the steam release.

Borderlands DLC is a fine example of this.

Both Steam and GOG don't have Securom.

Yes, the implemented Securom in the retail version of the game has an impact on the performance and the startup time of the game.
So, if you swap the .exe from the retail version with the .exe from the "GOG-version", you might get a slight boost in performance and the game itself starts faster with it.

But, the increased performance only occurs on PCs which have dualcore cpus. PCs with quadcore cpus didn't get much out of it except from higher minimum- and average-fps in some scenarios of the game.

Sources:
http://www.computerbase.de/forum/showpost.php?p=9938683&postcount=745
http://www.computerbase.de/forum/showpost.php?p=9938927&postcount=750
http://www.computerbase.de/forum/showpost.php?p=9938975&postcount=752
http://www.computerbase.de/forum/showpost.php?p=9939230&postcount=755
http://www.computerbase.de/forum/showpost.php?p=9939616&postcount=767

http://www.hardwareluxx.de/community/16852183-post756.html
http://www.hardwareluxx.de/community/16852492-post758.html

(They are in german, but what counts are the numbers ...)

http://forums.steampowered.com/forums/showthread.php?t=1901313
http://forums.steampowered.com/forums/showpost.php?p=22557262&postcount=5

Indeed, dualcore users are affected. Should've mentioned this in the first post. ^^

I'm not sure, but I think that dual core CPUs are still the most common, aren't they?

I find it amusing when people get so caught up in hating piracy with all their pure little hearts' might that they lose the ability to comprehend that an invasive piece of software added to one particular version of the game just *might* possibly have an impact on performance.

There is a difference now. Before we had only two options:

a) Buying a game which only version has Securom. So we'd never know if the copy protection lowers the performance of the game.

b) Try a crack. Possible, but what then? Running to the publisher / developer reporting that their game works better cracked? They wont take you serious and it wont count as official accepted fact.

This is the first time (as I recall) we have two official versions, one with and the other without the copy protection mechanism. So it's the first time we can go public with our findings with a strong possibility of being heard by the developer.

Polish Retail version takes 60 seconds to start with original exe.
It starts in 10 seconds after using GoG executable.