Only 13 people using Lighttpd. I remember the week and a half when that was the preferred deployment platform for Rails. That was a while ago.
I suspect that might be under represented by people using Lighttpd for serving static content, with something else like Apache serving the main page html (Ive got a bunch of clients in that configuration with WordPress running on Apache, and all the images/css/js/etc coming out of Lighttpd.)
That should also be true of nginx, but it's pretty well represented now.
nginx is not only good a serving static file but is a (one of the most?) common reverse proxy server.
I run nginx on my Pi for a personal site for friends, and Lighttpd on a VPS for a very small site with a few gifs and low visitors. The Lighttpd regularly goes down to like 5-10MB memory usage which is really interesting, whereas nginx seems to cache more in RAM. Either way, both seem to work extremely well for low RAM (and the slow CPU on the Pi).