I think the approach to on-line backup’s is a good one if you already have another one in place.
The first thing I usually point to someone asking me this kind of question is: Don’t even think about disconnecting your current backup autoloader, tape, NAS, SAN, whatever you have.
No one should take a third party backup solution (in premises or not) and rely only on that. You should always have multiple layers of backup’s.
I tend to use this approach if the costumer / budget stand for:
Primary backup: Disk imaging;
Secondary backup: Data archival
Tertiary backup: Internet / remote sync.