Cool idea and seems to work, but might be good if it was activated by pressing a button rather than just a visit to the page - I am now logged out of a number these services just because I visited the page - which is not really what I wanted!
A List of supported services: <a href="http://imgur.com/M1wGK99" rel="nofollow">http://imgur.com/M1wGK99</a>
You have to love NoScript :)