Several folks have e-mailed me with more Deep Throat speculations, mainly that the man in the garage was Ben Stein. The main evidence for this seems to be that Stein, who was a Nixon speechwriter late in that administration, was a childhood friend of Carl Bernstein. Arguing against that is that (a) Deep Throat met with Woodward, not Bernstein; (b) Stein did not go to work for the White House until after D.T. had begun supplying the reporters with info, and (c) Stein, to this day, speaks well of Nixon and asserts that there was no Deep Throat. He says that Woodward, for whom he has little respect, just made it up.
One might point out that Stein once denied he'd written the article for GQ magazine that prompted a libel suit from Joan Rivers. He eventually had to admit authorship when the magazine settled with Rivers…so he has, in a way, been an anonymous source. He also was the son of a high muck-a-muck in the Nixon administration so he could have had info to pass on before he got his job in the White House. Still, I just don't think he's the guy. It's possible, I suppose…but I think it's another example of reaching far to make it be someone we've heard of.