Donna,
I think he was kidding about dialup.
What version or type of Jungle Disk are you using? Workstation? Server.
Even if you had 500GB of data, once it is up in the cloud, the following day's backup should take around 15 minutes. JD uses De-Duplication, which is MUCH faster than incremental and certainly faster than differential.
There are cloud services which will deliver your data overnight using hard drives given it would take many hours to download a lot of data. So, it depends on why you are using it. If you are looking at an online site as a "mission critical, have to restore in the next hour" type of thing, it isn't. Most can't. I look at it as one more offsite backup repository. Say the building does burn down. My guess is you can download from JD faster than you can build a new building.
First thing, though, what type of JD are you using?
