Alexa does give a rough estimate on the volume of traffic but I don't know exactly how accurate the numbers really are, depending on who has the toolbar installed or not. If you ask me, that would mean that even more traffic is hitting a site because what about the surfers that do not have the toolbar installed? They are still hitting the site ....but not being counted. So yeah, I don't know for sure, but I have always followed it, but never took it very serious.
But sure, I still think it is relevant ...to a certain extent.
Just checked my paysite rank - 37,035
True Amateur Models Alexa Rank