For every possible decision theory, there is a "nemesis" environment - where it does extremely badly. That is no-free-lunch fall out.
A "nemesis" environment that feeds misleading evidence to a decision theory's underlying epistimology does not indicate the sort of problem illustrated by an environment in which a decision theory does something stupid with true information.
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).