Utility to save current selection or clipboard to a file
Open Automator and create a service "text2file" with the following steps:



After saving the service, you may choose any text (you don't have to copy it!) and in the context menu -> Services choose "text2file" to save the content to clip.txt on your desktop.

After saving the file you can add a shortcut for "text2file" in System Preferences -> Keyboard -> Shortcuts -> Services -> Text -> text2file

The screenshot above is taken in Automator 2.2.4/10.7 (Lion). If another system is used the steps might be slightly different.