Bug #59695, first reported on 2006-09-09. It’s all the rage in the last few hours due to various blog posts both new and old. The fundamental reported issue is the frequency that heads are parked under Linux (not just Ubuntu). Specifically, the parking and un-parking is happening several times a minute. Drives have a set limit to the number of head parks they can do before the internal mechanism wears out. Each brand appears to be slightly different but in the end, once the mechanism fails, the drive must be replaced. What people are reporting are laptop drives only a few months old having to be replaced.
Power Management has always been, in my opinion, a rather difficult area for Linux so in that sense this bug comes as no surprise to me. For the record, I do not endorse any of the methods included in the bug report although the predominate one did solve my own personal issues. I raise this here on my blog and Planet Ubuntu for community and developer awareness.
Alternatively, this could just be an evil plot by flash drive makers to demonstrate the value in flash memory over hard-disks.