Comet ISON Update (hot off the scope 30 mins ago):
The guessing game continues. Measuring the brightnes of a comet using standard photometry tools is difficult as the Coma is quite diffuse. Visually comparing it with other near by stars can be a better indicator.
The Minor Planet Center ephemeris tool shows it at Mag 10.1 which looks about right visually compared to the Mag 10 star in the image, the photometry reading in Astrometrica is slightly fainter, but this is not as accurate doing it this way due to the diffuse coma with in the annulus of the tool.
Anyway thought you might like to have a look at the brightness your selves and make up your own mind.