I don’t understand PageRank

My latest weblog El Canasto is a big success, with more and more readers every day. Every week a few other weblogs link to articles from El Canasto and therefore I expected my PageRank to increase, but to my big surprise Google decided to lower the PageRank for El Canasto last week. It went from 5 down to four, and I have no idea why.
Normally I wouldn’t care about it, but in this case El Canasto was about to enter in the Top 500 of Spanish weblogs –and I expected an increase of visitors when arriving to that point– but the PageRank is one of the factors used to calculate popularity. The decrease in PageRank set me back to position 650. I can only wait until I steadily grow again, or until Google makes another readjustment of the PageRank.
We depend too much on Google…