Caching doesn't help that much if you're only sending the subset of the font that you're actually using for a given page. I'm not sure the same font gets loaded from different places all that often either.
If the recommended alternative is for everyone to use the handful of known system fonts, we very quickly arrive at everyone loading the same fonts anyway. Increasing that pool of options by having some additional choices in a cache would be nice -- especially for those of us on less popular OS's. And having to calculate a font subset per page and transmitting it along with the content doesn't sound like a winning tactic.
