A long long time ago.
But 2 of my counterparts at other enterprise level networks use notes and they hate it. They have been fighting with management to move to exchange.
Everyone else I know uses exchange. We have several of them here clustered.
As far as power, Notes and Exchange is only going to be as powerful as the hardware they are running on.
Although I have installed and currently running a pvt clients exch server on a dual PII 350. And they are happy.
Exchange is one of those few products (MS and others) that actually conforms to the RFC's. And interchanges with almost all e-mail clients out there (assuming your using POP or IMAMP, obviously using it in native mode you have to use outlook).
The scripting/custom programming that can be done for exchange and outlook is pretty much only limitied to your programmers expertise and creativity.
Depending on which version you get, standard vs enterprise, will dictate how well it will scale. Standard has a 16 gig Information Store limit. Enterprise has no limit on the amount of storage.
I just know that 3/4's of the time when we get complaints from users telling us that there is a problem sending e-mail. It is usually because the remote system is lotus notes and is having a problem communicating with us. Just an observation.