I haven't really followed the mobile market closely, but from what I understand, RIM's strongest advantage was data security. (Is this correct?) It would be interesting to see what hardened mobile implementation fills this gap.
The thing is, that is kinda paranoid and normal businesses don't really need that kind of security. But when BlackBerry's were one of the coolest devices out there and also the most "secure" ones, RIM's sales-reps had an easy time selling them to a lot of companies. Again, not that they needed that kind of security, but more security is always good, and the device is cool, so why not, right? :)
Nowadays, this doesn't work that well anymore, because the people working at companies are just like normal people and just want to use the coolest devices. CEOs and managers are usually the first ones to demand that their iPhone works on the internal network, and suddenly the whole BlackBerry advantage isn't all that important any more.
I think the market of business who really need the kind of security RIM provides is a very small one.
For those who carries BB around and "on-call" would probably agree: productivity boost.