It's been mentioned many times that the -f option should not be used. Especially if you updated via slices. The fsid's for objects you need to backup might be higher than 9999. You wouldn't back up all the required objects in this case. You should either back everything up, or use the -l option. You can search for this.
This thread shows the options:
http://www.dealdatabase.com/forum/sh...ons#post125707