Yeah, same here. I would like to compare the most valuable numbers to something like HQ Trivia, which was far more expensive to run (even when they weren't giving away $X00k per day in prize money).
Something very special about it, a few items that jump out at me:
- No permissions nags or signup required
- Massively popular seemingly overnight, despite no multiplayer features
- Sharing your score is both cryptic / interesting to noobs and a big network factor
- The one-puzzle-per-day part seems to put bring everyone together
