Although I'm eager to try Shift2, I'm forcing myself to wait for the release on Steam.
Why? Because it looks like it will turn out to be a fun game to use for LAN racing. Not too hard core so my friends who aren't sim fanatics can still jump in and have fun. Racing online is fine, but having a few of us in the same room so we can exchange good-natured trash talk is even more enjoyable.
Anyway, to use it for LAN gaming, the most convienent thing for me is to buy a copy for each computer once it appears in one of Steam's great sales. And I want to make absolutely sure that they're all completely compatible. Mixing one store-bought copy with others from Steam might lead to version incompatibility. Don't want to risk it.
As a bonus, I don't have to keep track of multiple DVDs and boxes and codes, just multiple Steam accounts that I use for this purpose already.
TL;DR -- Please release on Steam ASAP!