It seems frowned upon to do so. The reasoning behind that it stops a lot large companies from using the code. JSON's don't be evil comes to mind. I personally

It seems frowned upon to do so. The reasoning behind that it stops a lot large companies from using the code. JSON's don't be evil comes to mind. I personally don't feel like we should coddle their legal teams, but it is a good idea to be careful with any license modifications.