If you only have one site that you can access the stats to, the recent Alexa change probably freaked you out. But I can tell you from running multiple sites, with stats on all of them that Alexa was wrong before. And guess what, Alexa is still wrong now.
In fact, if you advertise based on Alexa numbers, you are still shooting in the dark. All you have really done is given yourself a justification to throw away your money when you chose to.
It used to be, if you were marketing products in the internet marketing, SEO, web development and other tech based fields, Alexa number were pretty reliable. After all, most of the people in this fields know about the Alexa toolbar and use it. But once you moved away into sites that did not appeal to this crowd, forget the numbers. They only muddied the waters.
Now, who the hell knows how useful the numbers are. They are still off, but there isn't even a niche that I have identified where they are "on". Lets take a look at some true stats and the resulting Alexa numbers, shall we. Each of these are last months stats from Google and they are pretty indicative of the average, except for the first, which is this blog. Subtract about 1800 visitors from that one. And that even makes the Alexa numbers even less accurate.
And I ask, what use is a number if it is not even partially accurate. Alexa, just shut up. I don't want to hear your about your improvement. Your algorithm is idiotic. And there is no point to it. It's like if I were trying to lose weight and the scale were set to random. Why even use it?