Reasons I would get the new iPhone
1.       Exchange Active Sync.  Push e-lettering, contacts and calendar.
2.       A better mobile web experience
3.       GPS

Reasons I will NOT get the new iPhone
1.       $15 more a month than I pay for an equivalent plan. [I need to keep SMS service for all the paging that happens other than for work, and for MMS.]
2.       $100 penalty because I switched to AT&T in January, getting my Samsung SLM then.
3.       Purchase iPod Touch between then and now, not believing the rumors of the 3g iPhone. It is the fifth iPod purchased, the previous was only 1.5 years prior.
4.       I am not sure if Mail.app notes will sync to the new iPhone. [part of the reason I got the iPod Touch to start, a promise Apple never kept.]
5.       I only use the mobile web to poke via Facebook, which is not available in the iPhone flavor. I suspect I would not be using for much else.
6.       A ‘better mobile web experience’ is still not that equivalent to Interwebbing on the MacBook.
7.       Does the new iPhone offer MMS? I heard rumors it does not.

I might switch if I could get a discounted price by trading-in my iPod Touch. That #1 reason I would get one would make the phone way sweet.

/* update */ iPod Touch purchased 2008 April 26. Switched to AT&T 2008 February 7.