The initial VPS package I ordered did not have very much RAM so I decided to run Lighttpd. Since then I have upgraded the VPS to a pretty luxurious package so the RAM limitation hardly applies anymore.
I still haven’t moved all my websites from the old server to the VPS and I just realized that a big threshold is moving the web server configuration from Apache to Lighttpd. Now I plan to revert to Apache on the VPS before migrating more websites.
Lighttpd is not bad, but I’ll save it for simpler setups than my 20+ virtual hosts including multiple forums, blogs, wikis…