I've been dealing with removing Microsoft Silverlight for sometime and I really think that I should write it down because there's no "easy" way to completely remove Silverlight on my Mac.
So, this is how you remove Microsoft Silverlight on your Mac – under Snow Leopard
1. Remove the Plugin in ~/Library/Internet\ Plug-Ins/Silverlight.plugin
2. Remove Silverlight folder in ~/Library/Application\ Support/Microsoft/Silverlight
3. Remove the receipts (try using Command + F, type "silverlight") in ~/var/db/receipts
That should do it.