First, I must admit, I was a bit biased when I switched from my long time ownership of Treos (started at 300, traded my 650 in for a BB8703e). I had grown spoiled by the touchscreen and the interface.
That aside, I still could not find the Black Berry to be usefull or good at anything. On a corp level the BES I know is irreplaceable. But on a smaller, personal level, the unit did everything my treo could do, with twice the complication. The messages inbox is a horrible idea. I hated that my SMS, emails and missed calls AND voicemails all were in one central box. For someone who easily gets over 100 emails a day, it was a nusiance.
Also, the calls were horrible (sprint). They dropped constantly and the quality was horrible. No one could even begin to understand me in my office while on speakerphone.
That, and like I said, I'm just too spoiled by the touchscreen. Having to back up through three lines of text, or figure out how to "wheel" over to the letter I wanted was too much of a pain. On the Treo, I just touch, change the letter or word I want, and I'm off again. No clumsy fumbling with a wheel and extrodinarily long menus.
The one thing I can say I noticed about the phone is the Blackberry OS is pretty solid. Even my new treo 700 locks up almost twice a day. But, it's a small sacrifice in my opinion and the pros outweigh the cons. My emails come through my email inbox, calls are in the call log, and SMS are in a messaging client. And I can actually FEEL the vibrate feature when it's enabled (I never, not once, felt the 8703 vibrate)
One dissapointed (and past) Black Berry user, singing off.
See ya!