Bram Cohen, the creator of BitTorrent, has opined on Bitcoin over the years on social media (such as Twitter).  Over the last couple of weeks he has been increasingly vocal on some hurdles such as the increase in block sizes (via a hard fork) and the dangers of accepting and institutionalizing zero-confirmation transactions.

Last week he gave a presentation at the SF Bitcoin Dev meetup in which he covered a variety of alternatives to proof-of-work such as proof-of-steak (which he dubs “Cow systems”).