Here are the back-of-the-envelope numbers for June 17, 2013.
Today, Comet ISON is approximately 3.295 AU from the sun.
Comet ISON traveled a distance of approximately 0.013 AU between June 16, 2013 and June 17, 2013.
0.013 AU = 1,208,425.49 mi 0.013 AU = 1,944,772.32 km
That’s an average speed of roughly 50,351 mph or 81,032 km/h.
That’s approximately 13.99 mi per sec or 22.51 km per sec.
There are still 164 days till Comet ISON reaches perihelion.
Comet expert John Bortle forecasts that Comet ISON “will develop more slowly in the autumn morning sky than initially thought.”
Bortle also predicts that ISON should be visible to the naked-eye around November 10, 2013.