It's less than a year old but with Apache and mulitple instances of AOLserver running, I felt it needed the boost.
I already have dual head monitors ... I got myself a dual core Ahtlon X2 3800+ and increased RAM to 2GB. The only other processor available was the 4400 and I'm rather superstitious about the 4.
All I can say so far is that 2 heads are indeed better than one and I'm not talking about the dual head monitors. The dual core CPU really works and I feel it when I'm watching the latest anime torrent while toiling away on multiple terminals, look Ma no skips.
I had to fiddle with the Linux Kernel. A dual core CPU needs an SMP Kernel to be able to utilize both cores. With SUSE Linux, however, it was as they say "a piece of cake" with Yast.