If you have a Blackberry and a Mac .. read this ..

Sorry I havent caught up with the thread, but here's my $0.10 ..

1) WHY BLACKBERRY --
a) in a corporate environment, I can keep in VERY close touch (email, Chat) with my peers and customers and not have to be behind a laptop all the time. Also -- messaging encryption over the air is standard. There's about another 12 reasons to have one in this environment, but I wont bore you (unless you insist).
b) for a PERSONAL/Self Employed Environment -- Push email and wireless reply. Like Chris said above, other than this majic, the BB is a good PDA/Phone combination. (the integration of the phone book to the Phone is second to none). The respective carriers (Sprint, Cingular, Verizon, etc) all use the same "Blackberry web client" email service OEM'ed by RIM. So it is possible that you can have your .MAC email, GMAIL, Earthlink, Yahoo, etc emails come to your BB wirelessly. If you ran your own business and rely on email, this is invaluable.
c) as a PDA, I would say that (personally) it's OK -- it's at par with a PALM, and not as good as a PocketPC.
2) CARRIER INFO and BLACKBERRY "Lockdown"
Most major carriers these days (Sprint, Verizon, Cingular, TMO) know that they have to start offering better data services because voice is being consumed on other fronts. This is why you are starting to see other interesting services like Music Streaming, etc. If you are interested in these services, the BB is not the choice for a platform. The BB is intentionally "locked down" to secure and corporate oriented activities -- hence, no camera phones (Security risk), it's "difficult" to install other software (again, security), and depending on the security policies of your company that may run the Blackberry server that you would connect to, they can REALLY lock things down.

That being said, there is no other real competitor out there to this platform (yet). Once there is competition, and you want push oriented email to your phone, feel free to sniff out the other offerings.

BTW -- I have the 8700c and love it.

Mike