The Blackberry calendar is fine and for most people it two-way syncs well with iCal (I have had great success using PocketMac, Missing Sync, and the new Blackberry Desktop Manager). There are some people on the Blackberry message board who are having some calendar issues, so I can't tell you that it is 100% full-proof, but of all the syncing problems we BB users have complained about over the years, iCal is far and away the one with the fewest problems.
As far as the calendar app on the phone itself, I tend to view BB's in the same eye as Macs. They are very simple to use once you learn the tricks, and if you do get a Blackberry I would strongly suggest one of the first things you do is look up all the shortcuts to use within programs. Using the calendar app is a breeze when shortcuts are utilized.