For example, are there proportionally more Google employees from Caltech or more startups in YCombinator with Caltech graduates?
I'd bet P[At Google | Caltech degree] is greater than P[At Google | Princeton degree], but it's mostly explained by P[interested in CS | Caltech degree] >> P[interested in CS | Princeton Degree].
In terms of other measures of success, Caltech might lag behind some other schools. As a current CS undergrad, I only know of a handful of startups run by Caltech grads. As I said, this is changing, but it goes to show the impact of choice of metrics.
Since they are all based in California now, I would think yes. But since Larry and Sergey Bin are both from Stanford, I'd expect a disproportionate number of Stanford grads at Google.
In any case, one way universities market themselves is by looking at the average income of their alumni. Since Harvard grads often end up on Wall Street, I would not be surprised if Harvard comes up on top.
But you could argue that's just the financial industry connection. What if you restrict your search on science and engineering majors? Well then we already know MIT and Caltech are better.
Maybe financial industry salaries would change these rankings if they considered averages rather than medians, but a reasonable number of Caltech grads end up on Wall Street as well.