Friendship compatibility test

When bored, there's always xkcd...
Favorites (not in any particular order):

http://xkcd.com/378/
http://xkcd.com/297/
http://xkcd.com/849/
http://xkcd.com/464/
http://xkcd.com/833/
http://xkcd.com/341/
http://xkcd.com/350/
http://xkcd.com/327/
http://xkcd.com/371/
http://xkcd.com/138/
http://xkcd.com/458/
http://xkcd.com/290/