I have a growing collection (15ish tips at the moment) on using Apple's Aperture. I've been told that the information I am providing is very useful to people starting to use Aperture, or thinking about using Aperture, and it's saving them a lot of time coming up to speed.
[robg adds: Typically I'd just list an entry such as this in the Links section, but we have only a handful of Aperture hints here (and half of those deal with simply running it on unsupported machines), so I thought I'd add it as a general hint, so it can be more easily found with a search. I'm not an Aperture user, but I asked a couple of friends who are about the site, and they felt the tips were well-written and useful.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060709155637740