Since 2.3 came out, many players noticed a major FPS degradation; a russian player "Raze" made a nice find and posted it on WoW Europe Forums, he found ount that you can significantly boost World of Warcraft performance by simply opening Windows Media Player before starting up WoW.
Short non-technical explanation: Your computer usually reserves a certain % of the CPU for background applications. Having WMP opened changes this behavior and allocates all available CPU to WoW. Little to no CPU time will be given to background applications and services, therefore increasing WoW performance.
It worked for us, but according to that thread, its not working for everyone.
Thanks Csulok and Dolk for the tip.
http://worldofraids.com/