I use Clicky as my default analytics tool for a new site. It filters out referral spam automatically which, by itself, justifies the $10/mo for the basic plan (which covers multiple sites).

http://clicky.com or http://clicky.com/100950546 if you want to use my referral link.

Referral spam is just a waste of time, and if a site like Clicky can fight it effectively, I don't see why my Google Analytics is constantly littered with it. Gmail's spam filter is amazing, but their referral spam filter seems non-existent.