First off, Karmic told me that one of my hard-drives was about to fail. I've since discovered this is almost certainly not true. In the process of trying to backup the data on that drive to an external drive, while copying large quantities of data the screensaver froze the computer entirely, so that the only option was a hard reset. I'd only been using Linux for a month when this happened, and I didn't have the know-how to either revert to 9.04 or fix whatever was wrong, so I've migrated back to WinXP for the time being (slightly old machine without enough power for Vista or Win7).