Lets take a more scientific look at the YC generation of accelerators (which significantly differed from earlier incubators).
Since 2008 there have been only six consumer startups founded that have hit the billion dollar valuation mark: Instagram, Pinterest, Dropbox, Evernote, Groupon and AirBnB (you might choose to exclude Dropbox and Evernote from the consumer market).
Two of them are from YC, and Pinterest was founded by a YC alumni.
Since 2008 there have been only six consumer startups founded that have hit the billion dollar valuation mark: Instagram, Pinterest, Dropbox, Evernote, Groupon and AirBnB (you might choose to exclude Dropbox and Evernote from the consumer market).
Two of them are from YC, and Pinterest was founded by a YC alumni.