Even 50,000 is far too inaccurate. You can easily achive that with sites with no traffic. Set your IE homepage to your site, install the alexa tool bar and your rankings will rise well. Set your whole office and youll easily reach 50,000 I have had rediculus numbers like 1800% increase in alexa rank - change in traffic - 0-5% Uses of alexa? Finding out what sites your competitiors own, look at or are affiliated to. Writing bad/ good reviews on each other. Fooling those that dont know Stopping people from doing useful things harvesting emails and contact details of some sites. Cant think of much else.. The alexa toolbar (and I think IE used to have a default cookie from alexa on IE installation - though im not 100% on this) is how the ranking is calculated. http://www.hitwise.com provide much more accurate results if you really need them and some good industry stats and info too.
Yup alexa rankings mean sh*t professionally, although i have top rankings they are only good for bragging rights. There is numerous programs that work similiar to trafficswarm, people sign up with the alexa toolbar installed then have to view sites 30's a time and earn points in turn to display their sites. Add to that the amount of speculation about the alexa toolbar and spyware it really isnt important.
Holy old thread revival.. I guess when I asked this question 6 years ago I had no idea it would be utterly useless now as it was when I asked the question.
there is no way to tell in general it depends on the niche and the time you started and you are talking about. When I launched my first website I had a alexa of 1,5 million with only about 10 views a month but today you are starting with way higher ranks so the ones below 500k I'd say are worth way more and a good site has a rank below 150k I think as this will be more then 400 views a day.