Like you I was unsure whether a BB would be useful or not. I already had a good phone (G3 with email capability) and a Sony PDA. Both had their limitations however. The PDA battery was on the way out and a new battery would cost half as much as a new PDA. And the inpuit/screen on the phone meant email was toublesome.
I run my own business and wanted to have email access "on the road". The BB means I am not tied to a desk. I am not a business customer though - just a personal one.
I use the PDA apps - especially the calendar for appointments. I use pocketmac for blackberry to sync with my OSX machines. I miss the stylus input but the very useable trackwheel on the BB makes up for it.
I dont use the phone function as my G3 phone plan is very cheap - 4000 minutes for about US$25. I think the BB is a bit big to use as a phone and I would have to be very careful when I am sitting round the pool (thats one of the perks of being the boss!).
My BB experience has been a good one. I pay US$10 a month for the email and got a free PDA (the BB was totally free). Can't be bad!