Alexa for Online Marketers

If you're not familiar with Alexa, here is a primer on what they do and how to use the information they provide

Alexa provides traffic rankings for millions of sites. How do they do this? Millions of internet users around the wolrd have downloaded Alexa's toolbar as a browser add-in. Alexa uses the toolbar to gather information about what sites/pages are being accessed by its toolbar users.
Alexa then ranks the sites based on numbers of visits.

What info Alexa provides:
- Traffic ranking (for example, Google is 3rd), average number of pageviews
- Charts showing historical visit trends
- Daily Reach (out of one million internet visitors, x visited this site)
- Related sites ("People who visited this site also visited these sites")
- Sites Linking in (I prefer using the linkdomain: command on yahoo or msn search)

Limitations:
- Data is based on toolbar users who may have different internet usage behavior than the average user
- Doesn't provide data on # of visits, just reach and ranking. There has been at least one attempt at calculating # of visits based on Ranking. You can find it here.

What I use it for:
- A rough measure of the popularity of a site
- To find related sites. I find the related sites to be the most useful feature. Recently, I was trying to find potential sites for a client to advertise on. I found one quality industry "authority" site and then used Alexa to find other sites that people visited. This resulted in me finding great sites that I would have never been able to find by doing a simple web search. For this reason, I have installed the toolbar on my system and I find I pretty much use it daily.