Do I feel like these have been unfair? No. In each case I can perfectly well understand why I was passed over: I screwed something up, whether an algorithm on the whiteboard or incorrectly describing a certain data structure. While it's a bit depressing to read stories like this about SV firms competing to hire college students, I've come to realize that I'm just not good enough to get those positions.
Right now my plan is to stay where I am for a year (I do have an offer from a local firm, it's just not that exciting) and build up a portfolio of work. I've got products shipped out there in the wild but nothing I'm that proud of. However, a year of weekend projects will give me a portfolio of working products and (hopefully) make me more attractive to companies in Silicon Valley.
I'll be releasing my senior thesis project into the wild soon and the corresponding paper has already been accepted for publication. I've started submitting pull requests for open source projects on Github with bug fixes.
Right now I'm not good enough. A year from now, I will be.