I used lighttpd from 2007 until early 2009. Then the company I was working for at the time went to managed hosting for about a year, and during that time, we had to use Apache (possibly even with the prefork MPM). When we decided to go back to self-managed dedicated servers in early 2010, I chose nginx. What I remember from that time was that nginx was rising in popularity, and it was being used by WordPress.com. Also, unlike the 2007 setup, this early 2010 setup had a load balancer with three application servers behind it (using FastCGI I think), and if I remember correctly, it was easier to do that with nginx than lighttpd.