If you're using the chipset on intel boards, the SSD will improve general speed but it won't be as fast as your install on SSD.
However, in saying that... it depends what you want to do with the SSD drive.
I personally will install Windows on SSD drive, but my girlfriend prefers her games (World of Warcraft, Sims 3 etc) installing to the SSD for ultra fast loading times.
World of Warcraft loads fast, and rendering the world and characters is instant while Sims 3 has gone from a few minutes loading times to 20-30 seconds or what ever, but its a heck of a lot faster for loading games.
If you're just looking for a healthy all round boost, go with cache... but don't use the readyboost from windows.
Although you can setup a SSD for use with readyboost, its more aimed at smaller USB cache drives.