Traffic is easy. Profit is harder - especially if you make it clear from the outset that you're anti-advertising (See Reddit).

Whilst the growth is fun to watch, it's still only 37 direct queries a second, which is nothing.

Also, I know it's been mentioned a million times before, but the name is an artificial ceiling to growth. A large % of people have no clue what duck duck goose is. A large % of people see the name as amateur, childish and stupid.