I was interested in upgrading my laptop's hard drive to ext4 from ext3. Ext4 offers some features over ext3, and I figured that since I upraded to Kubuntu 9.10, I might as well upgrade the file system.
This blog post describes the steps needed to upgrade from ext3, without formatting the hard drive.
Unfortunately, I didn't unmount it before running through the steps, and I didn't pay attention to the fsck warning. My partition did get corrupt, and I decided to reformat and do a clean install. (At least I am able to create an ext4 partition, and it is nice to do a clean install every once in a while.)
Luckily, I was able to restore all of my data, since I have been backing up my files on Linux with JungleDisk. Also, I am able to restore my Windows VMWare image, since it is backed up to my Windows Home Server.