Last night I switched the Webserver/Load-Balancer from Lighttpd to Nginx.
It took about 5 hours to port 1065 lines of Lighttpd config to Nginx, but it was definitely the right decision.

The only disadvantage of Nginx is that it doesn’t support CGI ( which could be a big security advantage ).
I solved this for now with a Lighty listening on localhost and proxying all requests to CGI applications through it.

Concerning the performance I’m really impressed of Nginx.
It serves static files light years faster than Lighttpd, and with the fair load balancer module it kicks ass at load balancing.