When we first wanted to load balance web servers, we initially followed Rackspace Cloud's articles on the subject. They recommended using mod_proxy with Apache.  This took a little while to set up and even with countless amounts of config changes, every now and then requests would get lost and you'd have to refresh your browser to get connected again.  This was not a problem in a development environment, but is unacceptable when we wanted to go live with the service.  So we looked for a different solution and found HAProxy, which was not only easier to set up than mod_proxy_balancer, but is tonnes more reliable and quicker too.