I have just installed SBS 2011 at a customer site. Microsoft says that Backup will not consume much space, since it is incremental. Default schedule is 2 times a day, but as far as I can see, the incremental backup is only of the data disk (if customer has two or more volumes). This meens that if you follow the standard settings, you will have two full backups each day of the system disk, which will consume around 60 GB each day and fill up a 1 T B disk in 16 days.
Any ideas what to do about it. I persume you don't need a full backup of the system disk twice a day.