This isn't a bug with Photoshop, so I didn't log a bug. The "photoshopcs6_p1_mac_032112.dmg shows an error of -4960 when you try to mount it. The file size is 1,231,479,172.
That means that the download was bad and the DMG is corrupted.
You'll need to erase that and download again.
Thanks Chris. It's not often that a second download of a file would give different results, but in this case the second attempt gave a file size of 1,032,137,621, and that did indeed work fine.