Foreach removal of Magic Quotes PHP
If you are sanitizing your input just for the sake of sanitizing your input, you're wasting time (both yours in coding and the computer in execution). Do you need to sanitize $_COOKIE if you never use it? What about $_SESSION?

Only sanitize what you need, when you need it. Switching to a PDO system to have it sanitize your database queries would solve that aspect (and the #1 reason to sanitize).