I'd hope that I could use it for two years, but realistically with no 3G that would be a stretch. If it did have 3G, then maybe. But by then iPods like have 1TB HDDs and who will be content with 8GB?
Personally I don't think I will be spending $500-600 on a cel phone any time soon. Now when they have one that is a fully-functional Mac (a MacPhone, not an iPhone) then maybe I'll get one even if it is $1500. Imagine Garageband and iMovie on your phone, sweet! I was hoping the iPhone would have been more along these lines but sadly no.
I would also have liked to see some kind of stylus support, what ever happened to Apple's Ink? That went nowhere. I know the multi-touch is really cool and all but a drawing app or Photoshop lite type *** would have been really cool. At least something akin to NotePad on Palm OS. After all it is running on OS X.