I know of two people who have horrer stories about the DOS 6.0. 
That's 100% of the people I know with DOS 6.0. Both have
had to reformat their disks and start over.  One had drive D compress and work
fine, only to compress C: to have the thing choke, spit out an unintelligable
warning, and then hang.  All that was left on either drive was autoexec.bat
and config.sys.  Calls to Microsoft only met with busy signals.  After reformatting
the drive, I'm not sure if he had the guts to reinstall 6.0 or stay with a known
entity.

The other may have been a marginal drive, however, his upgrade failed,
he had to format a floppy disk at 6.0, format the drive, and then reinstall.

I make now claims since I was not driving at the time, however, be careful
and make sure you back important things up.