Looks like my information is either out of date or was incorrect all along. Bing seems to be the primary source. They seem to also have a crawler now, though it's not clear how much it really covers. Very cool. Slow and steady wins the race.

I posted this elsewhere, but I didn't get an answer. Since you work you work for DDG, you might know.

How long would duckduckgo have to grow at its current rate to become an actual blip on Google's radar? On the one hand, you're small. On the other hand, keep up a fast growth rate long enough and you get bigger faster than people's intuitions' expect.

https://duckduckgo.com/traffic.html