I got the impression that the OP's work colleagues had intended to continue using a hosted Exchange solution, so surely concerns about data privacy and ability load 3rd party apps don't arise?
I use such a solution (from
Premium Hosted Exchange 2007 services; Exchange Hosting whose service and support are first class) and, whilst I realise that they could if they wished audit my BB data traffic, that's no greater practical concern to me than knowing that my ISP could do the same, or that the police could intercept my phone calls.
So, to separate the two issues here, BIS to BES means not having to worry about USB, sync, backup, viewing sent folders, and takes BB performance and functionality to a whole new level.
But hooking a personal BB to a corporate server, that suggests placing constraints on something that should be all about freedom... but that's for another day.