Emily Lakdawalla at the Planetary Society also started a coordinated search effort last year. I don’t know if that effort is still ongoing, but her page on how to use HiRISE images in the search is still a great resource. It includes examples of known hardware, cosmic ray hits and other artifacts, and more tips on searching.
In addition to the list of images on the previous blog entry, these new images have been released: (we’ll try to keep this list up to date as more are released)
Thanks for all your interest, and good luck searching!
9/2/09: ETA new images released in September PDS release.