Well, I follow alexa....and quite frequently. I run a paysite that has an alexa rank of 18,583(
http://www.alexa.com/data/details/ma...teurmodels.com) and it seems to me that alexa accurately measure the amount of traffic that the site gets. I am always checking on my alexa rank to see if it is up or down. Of course, I have a traffic stats system that displays the details regarding the traffic breakdown and so on but yeah, alexa is good for showing other webmasters little details on your traffic. So yeah, alexa can be useful at times.