Up until a few days ago, DaniWeb has been run entirely off of one dual Xeon server. We just completed separating out Apache and MySQL into a web server and a database server, both identical Dual Core dual operon machines :)
Too much on my mind right now. Did a massive move of the site to a different server, and now in the process of upgrading to vBulletin 3.5, which should be completed sooner than later. With vB 3.5 come many, many added features, which may shed some light on the subject. Not to mention, I don't want to introduce any new hacks to vB 3.0 right now while I'm in the process of porting everything to 3.5. Expect the upgrade to go live before the end of this month.
The closest thing I've ever owned to a servar was a piece of who-knows-what my friend... found ("found" can and will imply woodland/illegal acquisitions)... it was biege, had wheels, and had a literally floppy drive. Not the mention it being the approximate size of a large luggage bag.