I can't say I'm unhappy about the prospect of ME2 coming to the PS3, but I'll only *really* be happy if the following conditions are met:
1. It comes with a version of ME1 adapted for the PS3, either on-disk or available as DLC (free to anyone who registers their copy of ME2, but at a price to anyone else, naturally). This one's the most important, overall.
2. Said version of ME1 has had its controls modified so that it's more like ME2 (less of the constantly switching out weapons RPG-style, get rid of the Mako sections or make them more tolerable, etc.). This would make the whole experience much more enjoyable, in my opinion.
3. Add in interactions with Zaeed and Kasumi on the Normandy in ME2, instead of the item-specific crap that was patched in instead of real dialogue options. This would be a nice touch, most certainly.
4. Allow players to install the game on their hard-drives so it'll run smoother and we won't have to deal with as many potential framerate issues. Not sure if players would need it, but I'd appreciate at least having the option to do so, for my part.
I doubt that all of these changes would happen - or any of them at all, honestly - but if they *did*, I'd absolutely go reserve a copy. If they just did a straight-up port to the PS3 without changing anything but the control scheme, though, I wouldn't buy it...especially if they just ported it and didn't also port over a version of ME1 (I didn't like its flaws, but I'd rather put up with it all for the sake of a more complete profile than just go without).
That's my take on it, at least.