Just a note from a long time iPhone user -- the iPhone is only fluid if you don't push it too hard. Try loading, say, 1000 photos onto one, and then scroll through the thumbnails. It'll only scroll smoothly if you go slow enough for it -- go too fast, and it'll force you to wait while it reloads ram.

And it isn't all that tough to cause an iPhone to crash, either; I tried receiving an e-mail that had a very large photo as an attachment (I don't recall exactly how large, but it was in the multi-megapixel size), and the phone locked up hard.

These machines are little computers. If you don't like the idea of managing how you use your little computer, you'd be better off with a product like the iPhone, featuring an environment so restrictive that it is almost impossible to perform a task that might tax the machine's abilities. But don't expect it to work perfectly even then...