Being the gadget freak that I am, one week ago I picked up a T-Mobile MDA. So far, I more-than-like it, not-quite love it. Here is my experience so far:

-was able to set up and sync (wirelessly) to all of my email accounts including my corporate email (outlook).
-seems to work just fine on the T-mobile wireless network, t-mobile hotspot, home wifi.
-slide out keyboard is fine, but I am still getting use to the difference in the keyboard layout between this device and my blackberry
-Got the data only plan from T-mobile, so I have not, nor will I probably ever, use the phone part of the device

Last week I took this device as well as my laptop on a cruise and was able to connect with no problem to the cruise line's wifi network and send a receive mail (even in the middle of the ocean). It worked so well that I never even had to use my laptop for email.

Bottom line (for me):
1. I may actually give up my blackberry and use this as a replacement
2. I may actually be able to leave my laptop home and just rely on this device for email (NOT for real work such as documents, spreadsheets, etc).

Only a about 1.5 weeks into the test so far, but this may just turn out to be a winner!