[kmike]

Well, I'm going to get to the basics on that.
The beauty of multiplexed web servers (lighttpd, thttpd, Zeus, nginx, etc) is in that number of connections isn't a choke point, their performance is usually disk (for static file serving) or CPU (for dynamic content) bound.
So there's _no_ reason not to enable keep-alive as it eliminates the need to re-open connection for the next request(s), and managing idle connections does not take up any resources for a multiplexed web server utilizing one of the advanced solutions to c10K problem like epoll, rtsig or kqueue.

Back to Apache, everyone's disabling keep-alive in Apache because every connection, even an idle one, requires one active Apache process or thread to manage it, taking up memory.

I hope it answers your questions.