Ever since I installed Mac OS X 10.5/Leopard, I've been unable to get iChat logs to appear in my Spotlight results. I used to rely on this quite heavily and it's been frustrating without it.
This morning, I spent a few minutes in Spotlight preferences and realized what happened: Previously, iChat logs were classified as "Documents," whereas in Leopard they're now "Mail Messages." My problem resulted from the fact that I don't care to have Mail messages appear in my Spotlight results. If I want to search Mail, I can do that right in Mail (and why, now that I think about it, can't I do that with iChat, too? Someone got a Spotlight-type widget for iChat itself?).
Anyway, it solved my problem, and I thought I'd share.