So back on topic, I started to run a test on this last year but 24GB was not sufficient for me to put WoW's data folder on a RAM drive and be able to comfortably run my 5 WoWs. I have another 8GB waiting to be put in my PC to do a real test, but haven't had a chance yet. (Plus I had to wait for a proper Windows 7 64-bit RAM drive)

Obviously, as has been pointed out, this is not a cost effective solution. It requires a server motherboard (I'm running dual quad-core Xeon) and lots of RAM. And to be honest, I'm happy enough with the performance from my WD Raptor. I just want to see how it performs. I'll share my results.