I think Alexa is worthless as Alexa rankings are based on only visitors count by their toolbar or from Amazon's A9 toolbar. And these tools are neither so popular nor being used by so many internet users. So it doesn't give the proper information about your website....
Many people use Alexa metrics to calculate how visited (popular) is any website. It works but it is not precise.
The less Alexa number blog/site has the more traffic it has. If you have good Alexa it means that you site is pretty good and profitable...
Well, now it's syndicating traffic details from few other sources as well. So, it's not so bad. BTW - Alexa is the only established yardstick is measuring a site's traffic. It's pretty important in my opinion. Cheers!