FastCGI is super lightweight and very powerful. If you're seeing errors like that you likely have a problem that requires fixing. Judging from your post it might involve excessive question marks in a regex.
I am running some basic stuff ... but notice the occasional 500's ... IRC / Web states that Pound with Lighttpd and Instances of Mongrel is really the best solution ... however, mongrel's site states that Lighttpd's mod_proxy still has issues....so I am really baffled with what is a proven solution... I am just gonna run some tests before I conclude...
