Google tool bar

On the google tool bar there is an icon called page rank. I usually don't pay any attention to it, but for some reason I noticed it this morning when I was booking an airline ticket. It claimed that on a scale of 1/10 the page I was on is only deemed a 2/10. The blogger homepage, which is owned by google, received a 9/10. The page I'm on right now only recieved a 4/10.

Who determines the importance level of the pages I'm on, and also when they were creating this toolbar, who is the guy that said, Oh, we need this useless tool on everyones computer.