Some people were talking about planets a while back and I didn't say anything because I thought someone else would answer definitively.
Well, seeing as no one did, I thought I'd post that IIRC, it was made known on Bioware's forums that there was going to be somewhere close to FOUR HUNDRED planets. However, those are almost all not planets you can land on, only places you can search/scan for loot.
In terms of land-on-able planets, there's supposed to be over 30, with each of them having some storyline, or, at least, considerable side quests.
Nothing definitive, I don't have the game or anything but I thought I'd let you know what I heard.
Loving the TV ad.