Alexa’s Data Accuracy
The following chart shows the accuracy of Alexa traffic stats for websites over time:
As you can see, not only is Alexa much more inaccurate than others, their accuracy is also going down over time, and currently at just 12% overall.
Note that above statistic uses gut feeling from a selected sample group (me) as data source. I might switch to the Blogoscoped toolbar as data source in the next release, though I haven’t yet decided which is more reliable.