Earskinz fit well, but aren't especially comfortable, and make the EarPods sound abysmal. The sound becomes garbled, echoey, and destroys high end response. I find that thin foam covers work reasonably well in terms of improving fit, and don't change the sound signature at all.
I like to think of EarPods as the earbud equivalent of portapro's, only much smaller and far more, ahem, portable. Unfortunately, neither portapro's nor EarPods offer any noise isolation. I can only use them at home or in a quiet library (lots of noisy libraries these days).
EarPods are the best freebie earbuds of all time, to date, anyway. I wonder if apple can come up with a design with similar sound signature but with superior noise isolation.