If you have an iPhoto library that you've upgraded to Tiger, you may have noticed that most of your iPhoto keywords and comments aren't indexed by Spotlight! It turns out that Spotlight only notices comments added by iPhoto 5.0.2 or later, which is why a search for my baby daughter's name only turned up 6 of the 550 photos I've taken of her.
Luckily, there's a simple fix to get all of your photos indexed. First, bring up the information toolbox (Command-I), and select the Keywords pane. Next select your entire iPhoto library (Command-A). Now check *any* keyword that has an empty checkbox next to it (make a new one in the preferences if necessary), wait a second or two for the change to take effect, and uncheck it. Voila! All of your keywords and comments are now indexed.
[robg adds: 550 photos? I'm guessing the baby isn't much older than a month, judging by my own history :)! There's another hint here on indexing iPhoto stuff; there's some evidence that the first method didn't work for some people, so I'm running this one as an alternative solution.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050516022840448