At one point, maybe a year or two into its service to me, I had to use an app to turn on the microphone and speakers to make phone calls, but this was fixed when I blew out the headphone jack--I think it was stuck in thinking that there were headphones attached. Two or three times, I've had keys become less reliable, but that's an easy fix--I just disassemble the phone, peel back the keyboard, and clean the contacts (acetone works well).
Yesterday, I thought it had finally kicked the bucket. We had an on-campus Fiesta event, and there was a small pool of bubble solution, and my son and I were making bubbles, and the Treo slid from my shirt pocket into the bubble solution. I checked that it didn't work, removed the battery, disassembled and dried it at home, and it still didn't work.
I then spent several hours looking at what Android options Sprint had for me. I wanted a large screen (4.3" is really the smallest I'd want, at least in wide-screen format) and a hardware keyboard (on-screen keyboards aren't very good for typing serious technical emails, especially if you need to use braces and the like--apparently a lot of people don't use them much). Alas, nothing met my desiderata. The Galaxy S II had an OK sized screen (4.5") but no keyboard, and the Galaxy S had a keyboard but the screen is little too small (4"). Granted, my Treo's screen is much smaller, and its keyboard symbol support isn't great (but I wrote an app that helps with that), but if I am going to upgrade, I'd like to upgrade to something that will satisfy me, rather than make me wish for something else.
I was planning to drive to the Sprint store and get a Galaxy S this morning, when I did the last check of my Treo and found that after drying out more fully overnight, it's now back to good working order. I wonder how many more months or years it'll last me.
Update: It's finally dead--see comments.