I saw a 900mb app the other day in the app store. I am sure it will not be the last or even the largest. Get what you can afford, but I would recommend the 32gb.
I was surprised how fast I filled up 12 of my 32gb and I have only had the ipad for a month
My wife's is a 16gb model, but she is a low tech user. She basically has a $500 Angry Birds and FlightControl box. ( I noticed she had landed 1200 planes in that game the other day. I am lucky if I make it to 100!!! )