Did you know that VS2008 has a great feature to remove any unused 'using' statements in your code?
Simply right click anywhere in your code file, select 'Organize Usings' and select 'Remove Unused Usings'.
You then end up with only the using statements you are actually using! (no pun intended ;))
Other options include sorting your current using statements, or removing and sorting at the same time..
Hope this helps!
UPDATE - One of my colleagues just pointed out that you can also do this (as well as some other great stuff) for all files in your project(s) using the PowerCommands for VS2008 add-in. Thanks Rick!