[Trigunflame]

Most server issues come by way of improper configuration, scaling servers is not always the best solution. You can just keep throwing hardware at something but your cost are going to keep skyrocketing, if possible it is always best to maximize the resourcefulness of what you have.

I have managed servers that average upwards of 2500 during idle times and 4000+ when busy with just using 1 dual xeon 3ghz/ht 4gb memory server using a custom compiled mysql (changes to mysql source)and lighttpd/fast-cgi / php 4.4.x/eaccelerator with offloading image/video to a seperate media server (we are talking somewhat huge files that would normally bog down traffic for page browsing); and the loads would generally stay around < 2.5.

When running database intensive applications such as vbulletin that is where most of your load is going to originate; if you setup your mysql configuration properly atuned to your server MOST people are just wasting money by running multiple servers.

Ps. If you have a large site with many Request/s, do NOT use apache as it is potentially the largest cause of swapping you can have even with a good setup due to the pre-fork model that 95% of people use.

Step into the new world, move to non-blocking IO servers such as lighttpd that use kqueue/epoll etc.. that have loads of advantages.
1. Tons less memory usage, these servers are built to run with small memory footprints yet handle more concurrent connections/request then apache could ever dream of.
2. They natively implement the fast-cgi model which is a Must for a heavy traffic site. mod_php is fine for small servers, but when you get into heavy traffic fast-cgi is the only Proven Stable platform for handling such loads.

Thats all from me on this issue