Two astronomy papers are up on the Nature website for open critique, the new experiment with open peer review that Nature is conducting.
Baryonic sweeping as the origin of the darkest galaxies in the Universe - Mayer et al
Fire at will.
I think comments are open to everyone, not just subscribers. Someone tell me if non-subscribers are blocked.
Comments and commenter IDs are public I believe.
Only comment I saw on quick browsing was on one of the squicky bio papers on sex... [sic]
Comments are vetted, but I think open for everyone.