Per the docs I believe that an easy migration is not even possible in 5.0. Still a wipe and reactivate.

As for the general transition, I just moved from a firm with Domino to a firm with Exchange. It is sort of surreal, in that you completely understand 85% of what is happening with the other 15% being completely wacky.

Like the Controller service in Exchange, I believe hosts all the multiple mail "agents", whereas in Domino it was the NBES component (single agent) that lived within Domino, and the Controller service was pretty much a useless appendage.

Yes and it is odd not having a Domino console.... just the BES logs to search and tail...