My bloggin' buddy Joe Bua of "I Am A TV Junkie" (link to the left, true believers!) pointed the way to a snippet from a Joss Whedon interview. He was talking about the success of the 'Dr. Horrible's Sing-Along Blog' experiment, and mentioned the leader of the Evil League of Evil:
"There's so much speculation about Bad Horse. Actually, the costumer who read it threw out some Bad Horse costume ideas. I was like, Ah, okay. It's a horse."
He was probably talking about all the rumors that Penny would turn out to be Bad Horse. But who knows? Maybe some nutjob making connections to 'Gulliver's Travels' and 'Mr. Ed' might have come to his attention as well!