I've been working on web site performance optimizations lately (though you might not believe it when visiting this site...)
I've come across a few useful performance-related resources that I've been using lately:
- Optimizing Page Load Time–An excellent overview of many issues that can affect web site performance
- Online web page benchmarking tool (webpagetest.org)
- Benchmarking APC vs. eAccelerator using Drupal (2bits.com)
And, for those who don't have access to an opcode accelerator cache (like eAccelerator or APC) don't forget to check out PHP 5's realpath_cache_size and realpath_cache_ttl settings. (Note: realpath_cache_size is ignored when open_basedir or safe_mode are enabled.)
Oh, and one last thing: Here's an interesting (and amusing) SlideShare.net presentation on hosting Drupal on Amazon EC2.