I found this article in which John Bischof speaks out against cryonics, so I mailed him, and he very politely replied almost immediately to say that cryobiologists consider cryonics a "faith based approach". Sadly he provided no more detail; I've mailed again asking him to write on the subject at greater length.

Update: he replied to my reply. I have also had mail from Ralph Merkle! Will make a new post on my blog with details later.