My wife and I purchased a 2012 Sienna XLE with the Premium package about a month ago. We have 1,100 miles on it already.
We considered the AWD model, but decided on the FWD instead. I will install Blizzak WS-70s on a spare set of wheels for winter.
Pros: Very comfortable drive. Smooth engine and transmission. The Sienna "fits" my wife who is 4'11", whereas she could not get comfortable in some of the other minivans we looked at. Steering is very simple, particularly in low speed situations such as parallel parking and school parking lots--some would argue that it could be considered "overassisted". My wife prefers that.
Cons: The 3rd row fold-down is not a smooth or seamless as the Odyssey. The hinges for the third row are visible in the cargo area, whereas you do not see them on the Odyssey. The 2nd row seats slide and the tracks are exposed. Some people feel that dirt, pet hair, kids crumbs, etc. can get into the tracks, but we have not experienced that yet.
We are very happy with the Sienna. We had a previous generation Honda Odyssey. I preferred the driving dynamics of the Odyssey over the Sienna, but the van is not my daily driver so my wife chose.
If you have not already, check out the forums on Sienna Chat or the Sienna forum on Toyota Nation for more owner details and reports.