Biggest improvement from the 650 to 700 is the powervision feature; it's much much faster then regular vision network, almost like lower end dsl line speed.
 I had a hard time setting up 700p as a modem and connect to internet. Now I am using pdanet for 700p, and it's very easy to use and i didnt have to deal with any of the advance setting and programing. ( you do not have to pay sprint for using your phone as a modem if you use this software).
www.mytreo.net and www.treocentral.com is good community to find review, download programs for Treo phones.
Since I am upgrading from the 650, all I had to do was install the new palm desktop software and sync it into the new phone.
Some programs will not work with your 700p such as any mp3 ringer management program or programs designed for 650.
Destaller is a good program for you to download uninstall programs, you may have to try every single program and reset to experience which program works with your new treo.
Besides that, 700P has 1.2 bluetooth ( better linkage). Overall I think it's slower response but slightly faster processing on most programs.
Oh yeah, when someone calls you; you can choose to send sms and not pick up a phone call.

If you're looking for faster internet connection, i would upgrade to this phone. Other then that, not too much upgrades.