I learned about definr a few days ago from reddit. I can't put my finger on it, but I really like something about this website. It didn't take more than a minute to realize it.
It could be the super-fast real-time dictionary results (reminiscent of the joy that is Instant Domain Search), but a slash of Occam's razor reveals a simpler reason: the mascot.
Wtg, definr. +500 points for the brilliant blushing mascot.