graeme_p - 6:31 am on Sep 7, 2010 (gmt 0)
Depends on your requirements.
For desktop use I only keep /home in sync. For a server you might want to keep other directories in sync as well. Where is your (valuable) data? Do you have time to do a re-install to recover, or do you need to be able to swap drives and keep going?
I only do this for desktop use so I cannot confirm how well it works if your requirements are more extensive,