we were at 8gig. and never were using more than about 2 gig of it. then we added wordpress on the pubcon.com side a year ago and we regularly max out the ram. (even though pubcon.com does one 20th the traffic of WebmasterWorld)
I stumbled across a post that I bookmarked (if I ever need it). It's called "Wordpress performance: Why my wordpress site is so much faster than yours". If you Google that query, you'll find it. The steps were a bit over my head, but I'm sure it will make sense to you smart guys. :)
I'd be interested in what you think of the article...
That's part of it, but the plain fact is that the style of FUNCTION'crazy/procedural php coding of Wordpress makes for slow executing code. (Especially when compared to zippy straightline/subroutine oriented code of WebmasterWorld's perl code). I would bet the average call to wordpress takes 20-30 times the amount of overhead code that we take here.
You can get around the mysql problems with caching. However, if you are running dynamic served ads or random content, then caching can actually SLOW down your server due to all the calls to produce a disked cached copy of the page. Obviously, you can do some other mem caching with mysql that lesson the hit of mysql, but in the end, there is only so much you can do.