Enough sites use Google Analytics wrongly (by including it at the start of the page rather than at the end of the page) that I have used AdBlock+ to block it.

Edit, since someone has downvoted this comment without offering a contrary opinion:

My comment is an argument against trusting figures on ad-blocking obtained using externally hosted javascript. If you host the analytics javascript yourself, no-one will be motivated to block you. And the reliability of statistics such as colour depth and browser window size are probably unaffected.