My referral software occasionally points me back to sgblog.com, which keeps a top 10 list of Singapore blogs. I've been on the list for a year or two, but have no idea how I got there. Not surprisingly though, XX is there, along with SPG and a model who appeared in FHM (against her will). However many other popular bloggers were left out.
Alongside each blog name was a figure in brackets. The higher the number, the higher the ranking.
Out of curiosity, I signed up for an account. Then I clicked on my own blog... and the figure in brackets increased by one.
So that's how it works - a simple clickthrough to measure popularity.