I am using swiftiply's evented mongrel + nginx for my site. I am tremendously happy with it and would be happy to spread the love (and config files). Email is in my profile.

how many boxes do you have?

Just one 4-core box.

i'll look in to it. no matter what i do, mod proxy balancer appears to not actually balance equally. i think i need to read more about it. and see if there is a mysterious setting.

balance=1

of the boxes, the first box always has a much higher load.

Mongrel, mod_proxy_balancer, and mongrel are all ass. Moving to nginx helped out a bit, but not really. Rails is lame because all the time you saved writing your app gets eaten up by rewriting it and doing sysadmin tasks with undocumented software. Sadly, for my next project I'll be pulling a Derek Sivers.