Are Alexa's traffic rankings accurate?

[apexis]

I do not consider Alexa traffic rankings accurate. Alexa ranking is just the count of visitors on the website with Alexa toolbar installed on their system.
If you have Alexa toolbar on your system and then visit your website few times in a day, you rankings will come up. This is why, Alexa traffic rankings are not accurate to me.

[MartinLedley]

Alexa are okay for a general idea of what websites are getting visitors and for how well your site is doing, but I wouldn't rely on it to give truly accurate figures. As a general rule, though, it does give you an idea of where the people it tracks are visiting, and therefore the general trend will be similar.