I've recently started playing through the first one and so far it's pretty fantastic.

Just played through this a few weeks ago, what a great game. Can't wait for the second.

playing through mass effect right now (slowly)
it is one of the most incredible games I have ever played, epic in every way

I've got to get back to my game on the Insane difficulty, the achievement for that and the stasis are the only 2 I'm missing and I find stasis almost essential for surviving fights on Insane so I'll get that pretty quick.
Overall I loved the game though, several little niggles and some repetition but a damned good experience. The Bring Down The Sky addon was pretty damn cool as well, the Batarians were rather nasty
Oh and also the interactive hardcore lesbian porn was worth playing for...

Any ideas if PC people are going to be getting this at the same time the X-Box crew are, or am I going to have to wait like six months after everyone else starts playing it in order to get my chance? Because while having a PC port that was nicer than the original X-Box version was pretty nice, having to wait for it kinda sucked.

Just had a quick look round the net, and while there is nothing definitive, most of the game sites and retailers have it down for March 31st 2010 on both PC and Xbox 360.
Not sure how reliable that is though, fingers crossed.

My god, i am sooooo looking forward to this game, Mass Effect was easily my favorite game of 2007, had the collectors edition on pre-order for I don't know how long, played it to death. Only problem with it is that is a huge universe, but there are so few meaningful things beyond the main quest. Having said that, really looking forward to this, love the angle they are taking, although that 'commander shepperd is dead' is such an obvious fake-out to increase interest in the new game. Looking forward to seeing where the story goes though.

Yeah I'm sort of hoping that they either cut down on the landable planets or make them a bit more interesting with a randomly generated town or 2 and a few mini-quests for the people there.

Played through the first one 3 times -- will probably go for a fourth right before the 2nd one comes out.
ME2 is probably my most single anticipated game at this point..

What meaningful choices did Mass Effect have, beyond the one at the very end (which turned out to be effectively insignificant)? I can't remember any that would affect the game in any significant way. The trailer looks good, but I'm a bit sceptical.

*Spoilers* (Not that I expect this to be an issue, but just in case...)
Well, one of the things one of the game designers was talking about was with the various NPCs in the game. Like "If this guy didn't make it in ME1, you won't be seeing him in ME2." So I assume this means that if you played through and, say, didn't manage to save Wrex, or chose to save Ashley over Kaidan (or vice versa) that you won't be seeing them in the sequel. I figure things like that will affect the status of your ME2 game assuming you import saves.
I figure they'll also carry over things like whether you saved the Council or not, or maybe they'll just assume one particular ending was canon, I don't know. Obviously, picking one particular set of circumstances as canon is the safer bet. (Like what they did with KotOR, but they could get away with that in KotOR a little more easily since the plotline of that didn't pick up with the same characters for the most part, while I imagine ME2 will.)

If they're reading the status of Wrex, Kaidan and Ashley, it'd be stupid to not read the status of the council, that's probably the most important decision you make considering the galaxy as a whole (though Kaidan/Ashley may be the most important to Shepard personally). I still have faith they'll continue just about everything with about the same status as where you left off (except being a few months later or so).
EDIT: Oh, and the 'stache is awesome.

the larger variables I can see (which are laden with spoilers so don't bitch to me about it):
Relationships (theres what, 3 you can get it on with?)
NPC quests (eg: If you get Tali the info on the geth and ME2 has a visit to the quarian migrant fleet, it could change a lot)
the human empire vs council membership choice
the councilman selection in the case of choosing the council
killing wrex
saving ashley / kaidan
maybe letting the batarian leader escape in bring down the sky
The cerberus investigation
selling the information on cerberus to the shadow broker
that criminal woman who wanted you to kill her partners so she could take over and be a less evil criminal
Frankly I can't stop thinking about that news report in the citadel lift that mentioned a production of Hamlet by the Elcor, I SO want to see that

(Yeah I just replied to this, but I just had to add another thing)
That's what they'll do in books (and any eventual movie/s - yeah I heard talk about that once), but in-game I think it'll depend entirely on what you have chosen (unless you decide to start anew instead of continuing from ME1).