My wife and I each have a 650:
Mine seems to be working fine but something recently caused hers to start having Hotsyn Exchange Synchronization failures.

No real applications have been added but I did hit on the Palm Desktop under hotsync - filelync over the weekend. This caused a loop that I couldn't get out of and had to unplug.

Somehow only hers has been affected? Any ideas on what filelync is? Any other thoughts on what I can try?