I'm thinking that 16GB should be enough for me...I just received an iPad 2 w/16GB last week. Previously I had a Kindle Fire (1st gen) that only had 8 gig, and I currently have a Nexus 7 w/16 gig since August 2012 and I still have 9 gig available. I mainly use my tablets for web browsing, emails, games like Zynga Poker, Sims Freeplay, WWF, and streaming music and videos. I only have around 200 songs at the most on iTunes as I buy most of my music from Amazon, or stream music from Pandora. Most of the movies I watch are streamed from Netflix, Hulu Plus, and Amazon. I own maybe 20 shows/movies in total between iTunes and Amazon, but have no desire to download them all onto my iPad all at once.
I may upgrade to an iPad 4 within the next couple of months for the better screen, and wondered if I should at least upgrade to the next size (32GB), in case the higher resolution, better camera, etc. takes up more space. But since I don't think I would store a lot of music and videos on it in the first place, 16GB should be fine for me (and cheaper)!