While Time Machine has simplified the process of backing up your Mac's hard drive, some of us still like to occasionally make backups on physical media, such as a CD or DVD, which we can store somewhere offsite. However, as MacOSXHints.com reader idoadam points out, burning your user folder straight to disk will cause an error in 10.6. But there is an easy solution, and the reason for the error is instructive:
When I was still using OS X 10.4, I used to back up my home folder to a CD-RW or a DVD-RW by dragging it to the inserted disc's icon; this worked without a hitch. However, after I upgraded to OS X 10.6, trying to burn a disc this way always failed. I'd get the error message
could not open the data fork of <unable to get file path> (-43), resulting in an unusable disc.
The file causing the error turned out to be ~/Library/Preferences/com.apple.sidebarlists.plist. It appears that the Finder modifies this file while burning the disc. The solution was simple: lock that file (open Get Info for it, then put a check next to Locked in the Info window) before burning. Just be sure to unlock it when you're finished.
OS X 10.6 issues this error message because it does not copy files to the burn folder before burning the disc; if the original file is still in use (as com.apple.sidebarlists.plist apparently is) while the burn is happening, you get an error. You'll get a similar error if you delete a file from its original location before the disc is finished burning, or if you don't have permission to access those files. So it's useful to keep this hint in mind whenever you're burning a disc.