I thought that multiple alarms had disappeared in the last version of iCal, but they're just a little hidden. If you click on the label "Alarm," as seen in the image at left, a pop-up menu shows "Add Alarm" and "Remove Alarm." This means you can have any number of alarms for a given event, which is nice for those of us who sometimes need to be reminded repeatedly.
[robg adds: Obvious to some, I know, but I didn't realize that there was a menu hidden there...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031222112126552