Schumacher was the "Stig" for that episode, since it was his FXX (parting gift from Ferrari when he left F1, rough gig)...
That said, the "Stig" has been rumoroed to be several drivers. I think they named Ben Collins as one of them (I believe he's a DTM driver), and there have been other's rumored as well, counting ex/present F1 drivers, etc.
I doubt the BBC would ever reveal the actual Stig(s), because it's such an integral part of the show (from the "mystery" standpoint).
As for the show itseld, Clarkson is a cnt. He can't do anything with an American car, or talk about America without some sort of slant/insult.
Here's a hint, if you don't like us, or our cars, stay the hell out.
The only reason I watch it, is because of the actual cars on the show. It's not too often you get to see that level of hardware being thrashed around.
Fifth Gear is much better in my opinion. Tiff Needle is a hell of a driver (an *actual* race driver, not some giant-meloned English t**t). He's truly passionate about cars, versus Clarkson's prejudice of anything "American".
If you can ignore him, the show's not bad at all. They tend to come up with some crazy crap quite often.