I had the exact same reaction when reading coverage of the demo day. Hopefully the ideas seem underwhelming because of the last part of Paul Graham's essay. In the "tactics" section he says, "If you want to take on a problem as big as the ones I've discussed, don't make a direct frontal attack on it." Maybe these YCombinator startups actually do have ambitious ideas, but they're starting out with something small and seemingly unimportant. Maybe in five years some of these companies will be reinventing education and communication.