From the looks of that macstories.com site (so far at least) Apps are ranging from as small as 4mb (Brushes) to 20mb (Yahoo! entertainment).
I have to assume more in-depth programs or games will be larger.
This is why I had to go with the 64. I can live with changing out video playlists if my 16gb or 32gb iPad starts running out of room. What about files created on the iPad though? Syncing those won't be as easy. 16gb is too small. Not sure why they started there (probably cost). 32gb is a sweet spot, but if apps are near 500mb, that won't last long.