i've had quite a long history with windows mobile phones starting with the Cingular 8125. My current phone is the Treo 750w, and if i can ever accidently drop it, i'll probably get an iphone or tilt.
I'm sure everyone here tinkers with computers and is so used to the day to day issues of having an ethusiast computer that you don't think twice about rebooting if something happens, or re-installing an app if it stops working. Well, if you get a Windows Mobile device, that lifestyle will transfer to your phone too.
If you set your phone to sync as e-mails arrive, and you get lots of e-mails, then you will have about a day worth of battery juice. You will need to charge every night. If you set it to sync manually, i could potentially go two days without charging. With both the 8125 and the Treo, i can go a week without problems, and i can also go a day where i'm constantly resetting it or powering off the internal cell radio and turning it back on to get back on the internet as it likes to refuse to connect randomly.
Built-in IE mobile is horrible and barely useable even in a pinch. So you will want to use Opera mobile or Opera mini for internet (both very very excellent).
3G is fairly speedy, but for whatever reason, the 3G radio sucks battery life. On my treo 750, I keep UMTS (3g) disabled unless i need it to extend the battery life. Seriously, no reason to have 3g when pulling up e-mails or using Opera mini.
Last week, i was on-call. My treo decided to refuse to receive any text messages, so i missed an emergency help desk ticket, yet when my boss called me to find out why i wasn't responding to the ticket, the phone part did ring, just no text messages. sigh.
The good parts. If you have exchange, the experience is pretty awesome. I also have it setup to connect to two pop3 e-mail accounts. Having your calendar, contacts, and e-mail always available and always synced is awesome.
Windows Live Search!!!!!! (go here on your windows mobile phone: wls.live.com ). Free download that has maps, directions, gas price finder, movie showtime finder, all with built-in speech recognition. I can hit the speak button and say "Arby's near harrisburg pennsylvania" and it will first confirm that i wanted arbys and the city/state was heard correctly, then it will display a list of all arby's with full directions, maps, and phone #s. Freakin awesome software. I don't print out google maps before leave home to go somewhere anymore. I just pull up the directions in windows live search.
At&T does support tethering but they don't make it easy to do so. You usually need to install some software and driver or get the driver working and setup dial-up networking with a special code to get it to cause the cell to connect to the data network.
I got remote desktop (built-in to Windows Mobile) and vpn (not built-in, 3rd party software) to work on my windows mobile phone one time. The start menu button took up most of the screen. So LOTS of scrolling to do anything.
For getting google imap to work on a windows mobile phone:
http://mail.google.com/support/bin/answer.py?hl=en&answer=78886