I still call foul when people say Alexa is easy to fake. "Faking" into the top 100K is easy - just visit your site self a few times a day. Maybe have a friend hit it every so often too.
Fake your way into the top 10,000 and you'll have my attention.
I slapped
this together late last year when people were saying how easy it was to fake. I tried every suggestion given and more - none of them got the site even close to the 50K mark, much less anything any lower.
As someone who spends some coin buying online advertising I will say that all other factors being somewhat equal the site with best alexa rating (assuming we're talking around 10K) gets my ad dollar over the site with the higher Alexa rating any day of the week.