As I’ve mentioned before, I like using iCal’s invitations to share appointments with people — especially since this lets them easily respond to let me know whether they 1) will attend, 2) won’t attend, or 3) are just “tentative.” Unfortunately, there’s no analogous tentative flag for the (seemingly endless) number of appointments and events I want to just pencil-in — you know, those times when you want to make sure to block out time for a call or lunch, but are waiting on confirmation from folks who don’t use iCal (or for whom it makes no sense to pester with an invitation). My workaround — yes, like many of these things — is really simple.
When I create the event, I just put a Spanish-language question mark “¿” (hit: OPTION-SHIFT-?) in front of the event’s title. Like so:

So, why’s this work?
¿” flag/characterLike I say, simple little trick, but it’s saved my non-Canadian bacon on a number of occasions.