Well WinSxS stands for "Windows Side-by-Side" in really simple terms windows creates a Hardlink to files here, however because hardlinks look like regular files to windows explorer, It seems that this folder is taking up a ton of space when really they are just glorified shortcuts. Windows uses these shortcuts to keep track of important system files, so deleting them could be disasterous.
There is one tool that can up slim it down slightly removing the out of date non performing hardlinks. You have to run the tool in administrator mode, here is the file. C:\Windows\System32\vsp1cln.exe remember after you have run this you will be unable to ever uninstall SP1 should you need to. Not that you ever would however I have to include that disclaimer. Run this program at your own risk, it made by Microsoft and I have no connection to it, however that being said it slimmed my WinSxS folder down a few Gb.
Post comments here letting others know how this tool worked for you. As a side know if you have a Vista where Sp1 was slipstreamed into it already when you installed it, this tool will probably not help you much.