Ok - This was helpful. I had asked something similar earlier. Bunch of Great replies.
I too have some 50 sites coming in but only two shows in Alexa. One is ranked 13,535 and the other is 666,378. The only thing they have in common is that they were one of the very first links that I got. (April 2003 - when I launched my site) Since then I have added a bunch of other high ranking sites. Some very high ranking and some not so high. So it might take much much longer to get any site to show which we've learned are stemmed from Google. As for Alexa, I think it's time to give Alexa a break. ( I have to defend a fellow San Francisco company) Alexa is not the answer to everyhting nor does it pretend to be. It is however, a great tool for someone like me who discovered
SEO about 2-3 months ago and have since been watching my ranking steadily and quite accurately climb week for week - hand in hand with my own website traffic stats. (very exciting and motivating to push forward) So don't use Alexa for what it' s NOT. This Forum Rocks.