I noticed this yesterday - I can not perform any updates via system update. The files download, but then I get a message about not being able to uncompress or expand the files, and to try again. I try again, and same happens. I thought something is up with the System Update, so I went to download the files manually. Again, the files download, and then I get the message "Mount Failed" in the Safari download window. I eventually managed to mount the .dmgs (after downloading the same file multiple times), but now I am getting the same thing with 10.6.6. Anyone knows what is going on, or what I can do to fix this? No other problems with the machine that I can see (MBP 2.66GHz, 4GB RAM, 256GB SSD).