Most of Apple's iApps are dogs.
Well, sure, Mac OS X itself is pretty much a dog (in its UI). Mac OS runs circles around it in many respects.
But that doesn't excuse 600K of calendars taking up 40% of my RAM on a 512MB machine (according to Process Viewer) in iCal.
Nor does it excuse that it takes more than 30 seconds to start on a G4/667. And about 30 seconds to move something from one (~300K) calendar to another.
iChat isn't very slow (how could it be?), but it is pretty buggy. It crashes a lot. iCal has some significant bugs too, though it's not crashed on me yet.