Here's my 2c...
I used a Macbook/Mail at my last employer. Had Exchange 2007, so Mail, iCal worked together well. Love it, simple, easy to use. Currently, at new employer [waiting for my new MBP to arrive 🙂 ). Using Outlook 2007; bloated, and feel lost. The only nice feature is the all-in-one view for seeing email, appts, and To-Do's. But can live without it.
Given the choice, I'd prefer Mail and all the other separate.