My sort-of-ish fix for people who didn't back up AND whose Mac shipped with Lion
For people who (sadly, like me) didn't use Time machine AND had Macs that shipped with Lion=no install media:
Same thing happened to me....Disk Utility claimed it couldn't repair the disk, "so back up as much as you can, erase the drive, and restore the backup". Wether booting from the Install image or the Lion recovery image, either installer freaked out about my Hard Drive that was perfectly fine up till the install.
I guess if you had Time Machine you could go back and try again, but I didn't (and will every day going forward haha)...eventually I got a really crude way to save your files and get to Mountain Lion. (Keep in mind I'm lucky enough to have a second Mac and an external hard drive in the house):
1. Boot the half-installed Mac into Target Disk mode while connected to another Mac through FireWire.
2. On the other Mac, it doesn't mount right away...go to Disk Utility, then File>New>Image from Folder
3. Browse to the "damaged" hard drive under Devices
And this is where it let me open it in Finder. Maybe I just didn't wait long enough, who knows.
4. Go and copy all your files/non-MAS apps into a folder
5. Disconnect and boot your problematic Mac into the Mountain Lion Install Recovery thingy
6. Plug in an external hard drive with 10 GB-ish
7. Run the ML installer and install it on the external drive
8. Boot from that and download the USB Recovery Disk Creator thing from Apple's website
9. Grab a thumb drive (with nothing you care about on it), run the program to create a recovery disk on it (you have to be doing this form the external drive because it loads the specific version of ML to the drive for your specific Mac)
10. Boot from that (the thumb drive), go into Disk Utility, and erase your Hard Drive (after making sure you got EVERYTHING you care about onto the other Mac)
11. Back in the Recovery Menu choose to Reinstall Mountain Lion, select your now-empty hard drive, and it goes about installing like it should have
12. Thanks to iCloud, my Email, Apps, Messages, and things like that were synced on right away...Load everything else back over from the other Mac
13. Sort them back into their folders...
And there. But this seems ridiculous that it's happening to a percentage of users at all (even if its super tiny out of that 3 Million) and that Apple wants to replace your drive. Nothing's wrong with it...Mountain Lion just put mine in a coma and Disk Utility is bugged up enough that even trying to use Restore to back up didn't work...
Hope this helps others with the problem, and Apple......fix this.