For me, the point of having an iPhone would be to continue the ease of use that comes with Apple products. Missing Sync works fine for me for basic syncing, but I don't use folder syncing or keep my iTunes playlists on my phone. I've tried it, but it just feels clunky, and not worth my time. I do sync to iPhoto, but only in the most basic way so that the photos I take with the Treo get saved to my computer. I'm sure on the iPhone all those things will be seamless and easy enough to use that I will take more advantage of the possibilities.
I also like the idea that it runs something other than Palm. I enjoyed the Palm OS until about 2002, and own hundreds of dollars of software, but it's way past its expiration date and I'll take just about anything that's not Windows. Having it be some version of OS X sounds like it should be a good thing.
I also hope that the OS X/Safari thing means the browser will be good. Blazer takes so long to render and is so limited compared to a desktop browser. I hope the mini-Safari will be more powerful.
However...
The lack of 3rd party software is very troubling to me as a longtime Palm user. The strength of Palm OS has always been that there are developers smarter than those who work at Palm who will come up with better apps, and will improve them after user feedback. Apple makes some great apps, but sometimes they're not powerful enough or I would just prefer them to work differently. If I don't have that freedom to choose, it will be a step back from the Treo.
I need 3G. I will wait until that's available. Again, it would be a step back.
And finally, I had a really, really bad experience with AT&T for six miserable years, which taught me that the most important thing about a cell phone is that it can make and receive phone calls. While I'm sure their coverage has improved in the four years since I left them and they merged and then un-merged or whatever, I still see evidence that their coverage is not as good as Verizon's (at least in NYC), and until I'm convinced that I can make a call everywhere a Verizon phone can, I won't go back to them.