Ok, I know MS says that 1 BB user represents the load of 3.64 users... But that is after enterprise activation, right?

In other words, when I first add a user to the BES and they are sitting there initializing, do they present a load on Exchange yet? if so, how much?

Where did you get that number from? Do you always go to Microsoft for competitors load info?

With Exchange 2007 or 2010 and BES 5.0.2 a BlackBerry user is pretty much equivalent to an Outlook client.

Activation is impacting the BES server and DB server the most. At some point the users contacts are pulled from Exchange and maybe some email (default is 7 days and 30 messages).