I've been trying to improve the performance of my teeny-tiny virtual web server host running Drupal. It's been an interesting process, as serving a moderate-volume site within a 128MB virtual Linux host is, shall we say, constraining :)
Up until recently, one of the web sites I run has been served purely with static pages. That worked well for some years, but they've noticed a large drop-off in traffic over the years, as more community-based sites with a similar focus have cropped up, and their static HTML, no-forums, minimalistic approach wasn't serving very well.
They enlisted my help for a site make-over, with a focus on improving usability and giving them the ability to have members of their organization participate in submitting articles and comments to the web site. Since it's not entirely ready yet, I'm not at liberty to share the URL, but along the way I discovered some excellent tips to increase performance.
One of my main concerns is that I've run a web site that has been DOS'd before (http://barnson.org/). This runs Drupal, and although it held up reasonably well under the strain, even with the cache module enabled, page return performance wasn't as good as it should have been under load. I began looking for an ultimate-performance-for-minimum-memory option, and think I found it in the combination of Drupal, jpcache, and turck-mmcache.
Configuration of Turck-mmcache, which caches the compiled PHP code from a site, has already been covered in the Administration Guide for Drupal, so I won't touch on it here. But after much searching, I haven't found anyone else who's used jpcache in conjunction with Drupal.