Never seen this posted on the forums, so here goes. WatchESPN hasn't worked from the Boxee browser for quite some time. Use your iPhone to airplay the live streams to the Boxee Box from the IOS WatchESPN app. The stream is pretty impressive on my end. I am using this as a workaround until ESPN maybe moves on to HTML5??
The only downside is the replay events don't seem to work at all.