After upgrading my OS X to Mavericks, starting Forman gave me a lot of weird problems. I stopped seeing my log outputs once guard started. Guard came up as a CLI prompt instead of running on its own, and it would restart tests constantly.
I'm not sure what changed, but the following fixed it:
guard: bundle exec guard -i
Adding the -i takes guard out of interactive mode. Makes total sense, but how it was working before makes me wonder. All documentation also says just run it without options. Very strange!