Also a Mac user here.
I had trouble using MobileMe for calendar and contacts.. I found (on Crackberry.com) another method which has been working beautifully for me AND wirelessly.
-Googlesync (available through gmail account) installed on your blackberry syncs between gmail and your blackberry.
-Busysync (for purchase of $20 after 30-day free trial) installed on your Mac syncs between gmail and iCal. As well as your address books on your Mac and your blackberry.
This wirelessly syncs your Mac to your Blackberry, with the gmail account intermediate, which is great because your calendar and contacts are saved on the internet (can't be lost!). Well worth $20.
Hope this helps.