CoreOS.com sounds super promising. I'm gonna be rooting for them. It's been a while since I last saw a real CS startup come out of Silicon Valley, much less YC. The action in this space seems to all be happening in Boston.
The point I was really making was that most YC startups are focused on solving for inefficiencies in various verticals (inspired by AirBnB I guess). Very few are focused on core CS. So I was pleasantly surprised to read about CoreOS.
Core CS/systems startups are definitely a minority in YC, but there are more than a few!