Alexa is a GREAT tool for comparing your site's performance compared to other's.
It allows you to punch in two or three URL's and see them graphed against each other.
For example -
http://www.alexa.com/data/details/tr...ckyourself.com
That link shows GFY compared to The Hun over the past two years.
It is showing RANK which means the rank in respect to all sites on the net. So GFY today is the 1,515th most popular site on the net and the Hun is the 814th most popular. Don't confuse RANK and REACH. Reach means for a given 1 Million People on a day, xxx number will have been to your site in that day.
Of course it isn't 100% accurate, as yes it relies on the toolbars (not just Alexa's) but it is the best tool there is for the job.
You haters just don't understand the tool.
I'd like to finish by saying, we as webmasters should support the tool - as it is SO valuable and would be a great loss if we lost it or discouraged it's use enough to reduce its accuracy further.
By the way - be sure to check out
THEpornTOPlist.com too ;)
J