Interesting to see everyone's reasoning for why they did or didn't get the larger capacity iPad. For me personally, I was going back and forth (pretty much since it's release date) whether or not I wanted\needed an iPad. Obviously I went ahead and eventually got one, but I went with the lowest model to save some cash and have the least amount of regret if I didn't dig the device (which I'm loving). A buddy of mine got the 64GB WiFi and admits he really only uses all the space for bragging rights and showing off. He has tons of movies on it to show people, etc. For me, the 16GB is working out fine so far. Like others have mentioned, I stream mostly all music and even my photos. I found a Shutterfly app (I've been using Shutterfly for a few years now) and I can easily view all my photos on the iPad, as if they were actually on it locally, great app! I have a few CD's ripped on the iPad and some photo albums. But other then that, I'm not using much space as of yet.
I do personally own a 64GB iPad. But it is a WiFi one so I can see some merits to having all the space. After music, photos, and apps, I used roughly 32GB. The rest I just filled with video.
I think with WiFi only unit, it's a lot more important to have more disk space. Next time around I'll be getting a 3G one.