The Treo is an awesome machine. IMHO it is the first device I've seen that really got the form factor done right. I'm always looking to consolidate gadgets and I strongly considered going back to Palm when that was released.
Three things held me back from buying one:
What if my palm wakes up and drains my battery, then I can't use the phone? Does this happen to you? I've never gotten an answer from anyone as to whether this could happen or not...
No wifi.There has since been released an SDIO wifi card, dunno if anyone has tried it on a phone yet. I would have expected poor signal quality and power in such a small form factor but one of our clients uses the cards with ipaq hardware and they work very well.
I'd like to think that I'll treat myself to upgrading one of my toys ever other year and this means a new phone or handheld, either of which would make the Treo a half useful brick. My service is through sprint and their phones are flashed, I don't have the luxury of being able to move my GSM chip from phone to phone. If I did, I'd have three or four phones to juggle depending on what hardware I expected to use or whether I wanted to travel light that day :-)