I'm on my fourth 650 (they keep having odd issues and I keep getting free replacement units). I can't wait to get rid of it. My Treo 300 was more useful and reliable. The 650 randomly reboots, the current one refuses to sync with either my Mac or my PC, regardless of the connection (IR, serial) or back end (Missing Sync, Hot Sync). I'm tired of rebuilding my contacts. In fact, I just quit doing it. Since I can't sync, Docs2Go is now DocsHaveGone.
Texting & the like if still tolerable, except that the keyboard on the latest one is going flaky on me.
The OS is, to put it politely, mature. My first Palm unit in 1997 was no less functional, and had better speed. The batteries did die in no time, but still.
I do NOT think the Treo line is bad, I just think that Palm/PalmOne/Handspring/Palm again have fallen behind by a good three years or so. I'm switching to the iPhoine for a number of reasons, but I already posted them here:
https://forums.macrumors.com/threads/287934/
Personally, I would've rather see a co-branded Apple/Palm unit. Hell, Apple shoulda bought Palm and cleaned house on the competition a couple of years ago.