As Zed Shaw pointed out, someone appearing to be Homakov has posted a comment dating back eight years. Is Posterous vulnerable as well? If so, that may not be Homakov, of course, but his twitter comments are consistent with him posting it.
Yes, one of Egor's comments in the github bugtracker had a small (but presumably not exhaustive) list of other vulnerable sites. It included Posterous.
https://twitter.com/zedshaw/status/176497720817762304