In this weekend added a SSD to one of my PCs.
I never used one.
My choice is Intel x25-V 40 GB. 100 Euro. Bought in local retailer.
Performance improvements are really good for WoW.

Generally this Pc manages 4 WoW instances.

PC host specs:
It s Dell XPS 420, upgraded in many components, Quad Core - 8GB Ram DDR2 - Video Card ATI 5770 1GB. Monitor 24" 1920x1080

followed suggestions, copied wow folder in SSD.

Great!
Input lag looks better, Game(s) faster.

Thinking to use one for OS, when in future build my new PC