In the FCC statement Alexis (YC Partner) mentioned 3,000 new jobs.
To put this in perspective, SalesForce employs ~12,000 (4x that) and has roughly the same market cap ($30b).
IMO, if I were YC I wouldn't be touting this number (nor am I indicating that they do currently). What's probably more important is how many new markets have been created, and therefore jobs, due to YC companies. A number which will be extremely difficult to measure unbiasly. Otherwise, this simply reinforces the notion that software is eating the world and developers are paid too much.
That was something that stood out for me in Alexis' statement.
At a $30 billion market cap, that's $10m per employee. I think that number alone is enough to indicate that YC isn't creating jobs as much as it is deriving value from software killing jobs. (They'd phrase it better, but any software making things easier, faster, etc will require less brainpower/ employees.)
The counter to this is either talk about the bubble making all valuations ridiculous, or that these companies are currently pretty small; If they grow to create or lead new industries, jobs will likely be created, and market-cap-per-employee numbers fall.
That would be only 7 employees per company on average. I'm sure there are a lot that never got past the 1-2 range but there are also Dropbox and AirBnb on the other end. Those two combined have around 2,000 employees according to Crunchbase.