This short incident report from Comodo is fascinating; in particular, check out the last line!
This nice summary report over on Freedom to Tinker does a good job of summarizing what is currently known about the event.
The Freedom to Tinker report links to this awesome post by Jacob Applebaum over at the Tor project discussing more details.
There are also short posts from Microsoft, Mozilla, and Google.
This is all very interesting, and I suspect we'll learn more about this in the coming weeks.
For now, though, I instantly wonder (and presumably others do as well): is this the first salvo of a Stuxnet counter-attack?