Uptdate 10am PST: ISON will encounter maximum temperatures and gravitational shear forces within the hour (about 10:40 Pacific). Latest images still show something is there, but there are debates as to if the comet nucleus is in one piece.
The comet was brightening very nicely until early this morning, when it has suddenly, dramatically darkened - very unusual - which could mean the comet has fragmented. If ISON survives, we may see a beautiful tail at sunset, possibly tonight, but more likely tomorrow.