Urbansory - that's actually one thing I really prefer about apple mail - that it's just a mail program, not bundled with calendar, addressbook and such.
I find MS Outlook/Entourage to be too much like a swiss army knife - it's got lots of semi-functional stuff built in. If you want a corkscrew that won't mangle corks, a can opener that won't slice your thumb open, or a saw that will cut wood before next week, you carry the real thing.
Anyway, one thing I find slightly annoying with iCal, and it doesn't seem to be really fixed, is that events cannot span midnight. Since my shifts at work sometimes do just that, I have to make two events, one till midnight, another starting midnight the next morning.