Wow, so many 32gb ipads. Who buys those? Seems to me you're price sensitive or you aren't, and you want disk space to dump all your stuff on it or you don't care too much. I don't quite see the use case for the middle ground.
I have a 32GB original iPad. If you want to be able to have all the pictures you can imagine having, but don't care too much about having your music collection there, then 32GB might be a good size. iPad form factor is great for photos. It's a bit big for a music player. This was my thinking.
Another reason: if you have a 32GB iPhone, then you could sync the same content subset with both devices, which might be easier to maintain than two sets of content for both.
I picked up a 16GB model yesterday, but I would've sprung for the 32 if they'd run out of the 16GB models. It was probably sufficiently important to me to have a black version that I would have picked up the 32GB black iPad before a 16GB white one.
This is how a friend rationalized it: He wanted to buy the 16gb 3g model, but realized that some of the games e.g. fifa 2011 run close to 1G in size. Naturally, if there are 10 of these apps, you would run out of space on the 16gb model. 32 seems like a good middleground, which is what he went for