We have found that generally by the time someone discovers they need to restore from backup, the daily backup has already been overwritten.
For this reason we run a daily incremental backup that keeps snapshots for a week. Rsnapshot is an excellent tool for doing this. It uses rsync to copy the files into a directory, and detects whether a file has changed or not. If the file has changed, it saves a copy, if it hasn't changed it just makes a hard link to the previous day's backup. This way you don't take up any more backup space than you need to.
Large IDE drives are so cheap now that there is no excuse for not keeping good backups.
Regards,
Erek
P.S. I wouldn't trust the WHM backup script to back absolutely everything up. pkgacct tends to leave things out like counter data and mailing lists.