“Alexa largely uses data from those people who have their toolbar installed (how many people do you know use this? - I don't know any)
”
I actually really like Alexa, and yep have the tool bar installed

Unless everyone is transparent and freely shares their analytics, the likes of Alexa is one of the few gauges available to compare yourself against competition. In our industry for example, it's interesting to see that we have similar traffic curves.
It's not perfect, it's data set is limited, but on the basis that the number 1 site is Google, and a 5 visitors a day blog will rank about 8 million, it's pretty easy to see who is talking hot air when they claim to have 1 million visitors a month, and have an Alexa Ranking of 15 million
So for me it's a quick and easy tool, especially when it comes to doing 10 second analysis on the latest and greatest partner offer to arrive on our doorstep
