Gives you a rough idea of the higher ranked traffic sites, however not so great for smaller websites, would be great if they offered more on incoming links.
Shame they have starting charging for this as well :(
alexa toolbar contains spyware and adware.
since end of 2012 curios ranking methods- not to compare withe real statistic for instance from google analytics - aleva time is over it give a lot of better tools with
real ranking and traffioc methods !