The problem with a web server is that I'm not sure there's much interesting inter-process communication which I think is where erlang would really shine. Sure you can spawn a lightweight process for each incoming connection, but after that?
Most people focus on Erlang as an easy way for multi-core/multiprocessor and distributed computing and it is wonderful at that, but the core of the language is a pattern matching engine that is simply amazing.
Also, anyone who thinks that Erlang is slow with regular expression should convert the regular expressions into a binary and try some pattern matching. That tends to be more of the Erlang Way of doing things ...