A couple of quick observations:

* Three of the ten unicorns (Airbnb, Dropbox, and Stripe) were funded by Y Combinator, while a fourth (Pinterest) was founded by two-time YC alum Ben Silbermann.

* All of the unicorns are headquartered in California. Eight are in "Silicon Valley" (i.e., the actual physical valley plus San Francisco), and two (Snapchat and SpaceX) are in Los Angeles.