Optimizing WordPress Performance

I've noticed that certain plugins seem to cause WordPress (WP) to run slower. PictPress, for example, seemed to slow down page generation by quite a bit. However, it might just be that the server load on the weekend is lower.

Still, I'm curious how to optimize WP, or to find out what's slow. A couple of tips to speed up performance I found:

• limit # of posts shown per page
• don't use posts-per-category counting
• hardcode links
• use xcode or some other profiler to find out where all the execution time is goin
• don't use the cgi version of PHP. Though my host's customer support said it shouldn't be slower when I asked before. lies?

The gist of this seems to be: limit the number of database queries and text processing as much as possible.