I don't envision DL as ever becoming a popular format. I've never purchased a disk. I purchased LOTS of CD disks and DVD disks when they first came out.
Before DL drives were released, my reading of the technical issues of DL pretty much convinced me it was not going to be popular. It seemed like DL would be full of concerns about disk life and compatibiliity.
And, yeah, I'd be very leary of trusting DL with my data. Even if it was used for backup, I'd want the data somewhere else, too. I've seen too many CD and DVD disks fail without warning. DL would have to be even worse.