> you could perhaps measure the level of difficulty of finding your identity

Here you go:

http://diyhpl.us/~bryan/papers2/security/Towards%20an%20info...

http://diyhpl.us/~bryan/papers2/security/Towards%20measuring...

http://en.wikipedia.org/wiki/Degree_of_anonymity

Also this is fun: http://www.gwern.net/Death%20Note%20Anonymity