Dave Fetterman has put together an excellent set of recommendations for string comparision practices.  Now I am really pleased by this because:

• these recommendations are going to help you to avoid some nasty security weaknesses that might otherwise plague you
• you get to use ordinal based comparisons more often and they are by far the fastest and cheapest

Speed and Security?  Say it isn't so!

http://msdn.microsoft.com/netframework/default.aspx?pull=/library/en-us/dndotnet/html/StringsinNET20.asp