Curiously, the fonts on that page didn't render particularly well for me (Vista/Firefox)

http://imgur.com/uHeAq.jpg

Unfortunately, for me anyway, the text on that page is really difficult to read and seems somewhat blurry. Perhaps not the best example...

On that site I can see a sort-of flash of unstyled content as the font loads, but that doesn't seem to happen on Typekit's own pages.

It depends on how fast Typekit's server responds. I'm sure it is extra slow today. I did some unofficial benchmarks on the service while it was still in beta:

http://iloveusability.com/usability-review/typekit/

It'll be interesting to see how well their servers perform under a heavier load.

That's put me off a lot; I'd expect them to be using a service that is very stable to scale now they have launched.

The fact their own site is intermittent today is worrying.