It's not the easiest to use, but it's the most usable mobile device I've found. I use pssh, which gives me access to all the keys I've ever needed without opening up the menu, between the keyboard and the onscreen keys.

It probably helps that I use it every day to ssh to my shell and reattach my irc session. Doing this means that I got practice so when I had to use it for real work I wasn't spending a bunch of time trying to figure out where certain characters were.

Now I just have EVDO in my laptop, so I pull it out instead of the phone. Still, the phone has saved me a time or two, especially when I didn't drive so my laptop was not in the trunk.

As a smartphone the treo falls flat in a lot of area (no multitasking, shitty web browser) but it's easily the best device for quick fixes in the field via ssh.