So in looking at the results so far from both the "Most Played Classes" and "The Classes that Nobody Wants" threads, some patterns have begun to emerge.
Right now the rogue is clearly the most popular class, as it leads the voting in the "Most Played Classes" and has the fewest votes in "The Classes that Nobody Wants."
The monk is probably the most unpopular class, as it has the fewest votes in the "Most Played Classes" and is a close second place in "The Classes that Nobody Wants." The ranger actually leads the "Nobody Wants" poll but it is polling much better than the monk in the "Most Played Classes" poll.
We could speculate as to why the rogue is popular. To begin with, I think cunning action is a shiny prize for character optimizers. It is also a relatively simple class which doesn't have to muck around with spell lists, so it is friendly for inexperienced players. The stealth/sneak attack aspect adds a bit of strategy which might appeal to some over the more generic fighter. Finally, the rogue perhaps more than any other class suggests an "edgy" and/or "anti-hero" type, which seems to appeal to a lot of people.
As for the monk's apparent unpopularity, to be blunt I have not seen one who contributed much to the party, even if they were roleplayed well. Some were a flat-out waste of space. I'm sure there are other reasons but frankly it has gotten to the point that I cringe slightly when I first see one at the table and wonder if it will be dead weight.
Rogues are indeed one of the most popular classes in my local gaming area. Monks appears at about an average rate (to my chagrin).