I use Mail with the exchange server at work.
It works beautifully with exchange server!
If you want to sync iCal & address book to exchanges calendar,
this program has been working well for me.
http://www.snerdware.com/groupcal/
I've tried Entourage... and loathed it. The lack of rich text in it & outlook is a huge complaint for me.
The Mail app is elegant.
Although I can hardly wait for the upcoming upgrade to it.