Thanks for everyone's suggestions. I've taken most of them and done some other tuning; I'll have to wait and see how much things have improved. If they haven't improved much, I'll be back on Monday. :)
I'm a little late to the party, and this is sorta off-topic, but you may want to check this out:
http://www.day32.com/MySQL/ It helps quite a bit for tuning your MySQL install.
