Here is an image (enlarged to 150%). the impact markings are near the bottom at centre, and Ganymede and its shadow are also visible:

Visually, through the eyepiece at 285x (LX90 8"SCT), I could see the black impact markings. Though it was small in the eyepiece, it was unmistakably a new feature.
Yesterday's conditions were much better. Here is one with the Great Red Spot (taken on 28 July 2009 at 1612UTC):
