I should be studying for finals, so I'll make this short and sweet and in bullet-list form. If you're in the DFW area, head over to Moritz BMW in Arlington on a Monday afternoon - they won't have a damn thing to do and they'll be thankful to get to take you for a spin.
-Size: I still don't think it looks very much bigger on the outside, but the only place where you get the definite impression of increased interior space is the backseat. It's now got a 'comfortable' amount of legroom whereas the E46 had 'doable for city trips' legroom. Road trips for 4 are now bearable in the E90.
-Electronics: The center console sans iDrive is fantastic. It's very easy to move through the increased number of options (BT, aux input, etc.) and everything's just as easy to use as in the E46. Also, the demo I got of voice command worked flawlessly, it even understood what number to dial without messing anything up.
-Motor: The 325 motor is about what you'd expect. It's a little better in pretty much every area. Slightly better mileage, slightly gruntier when punched, slightly better throttle response, and yet much much quieter at idle. Oh, and slightly faster too.

I drove a Step so I can't comment on anything manual. Having a six-speed surprised me though, as I could often feel it shifting out of either 1st or 2nd in the middle of a turn. All things considered, though, it's a good change and it makes the car just a teeny bit 'faster' overall.
-Suspension/Ride: Here's where things get scary. As my sales guy so eloquently quoted the official line, "they designed the suspension around the run-flats." And it's pretty apparent that they did. The ride isn't uncomfortable, but the resultant ride is a bit too soft. Drivers: know how when you go over a pothole and the steering wheel jerks in one direction in response, and it always surprises your friends? That jerk is now less than half of what it was before - and this car wasn't running Active Steering. That's not to say that the steering felt disconnected. In fact, it felt about identical to my E46. But while cruising around the city, the ride felt much closer to something Japanese than German. Sport Package might be necessary for most of us this time around.
-The Conclusion: It's undeniably the new 3, and we'll find it mostly good, but the Festers here will find plenty of new things to try and tweak on the forums.