Two years ago, PalmOS was more stable. This is NOT the case anymore, unfortunately...

Windows Mobile is an improvement over PalmOS. I have access to several versions and it's amazing how much more stable Windows Mobile has become over Palm in recent incarnations, as long as some rules are followed...

The OS has its own disadvantages, but it has other advantages too -- It's also much more multitask-friendly.

I predict Treo 700 is probably going to be a very significant improvement in stability over Treo 650. I'd bet the whole bank on it, based on my multiplatform handheld experience. I have access to dozens of handheld computers where I work.