From CIOC (the NASA Comet ISON Observing Campaign):
Will it be naked eye visible? When? How bright?
This is definitely the toughest question but also the most frequent. We still don’t know if it will be naked eye but based on its current brightness in the LASCO images – which is around magnitude +5 and fading – it does seem unlikely that there will be much to see in the night sky. I suspect that some of the outstanding astrophotographers around the world will be able to get something, but I doubt it will be as spectacular as before perihelion. I hope I’m wrong though.