Loaded question. For me and my clients, I explain all the options to them, make sure they understand the whys, hows, and costs of each option and then let them decide. While I certainly know more than my clients about computers, they're adults and as such should be able to make a rational decision on how important their data is. I've certainly had clients come back months/years after the fact and complain because they've lost data and have no backups due to their own decision, but what can I do? I do what's in my power to recover data including (with their permission) taking it to one of the several data recovery centers here in my area, but sometimes data just can't be recovered. I tend to recommend SOME kind of backup for people and despite my repeated warnings data gets lost.
All that being said, I think you have some good ideas. I tend to image any drive I'll be working on in the event something goes wrong during the process of fixing the computer. That's for my protection. I have a modest quad core processor "server" in my shop with lot's of disk space available for customer images and will usually ghost the drive to the network drive directly, depending on the size of the data, or may even simply ghost it to another physical drive. Obviously for simple things I won't image the drive, but for major non-booting situations I will. Once the computer is fixed and returned, I'll usually keep the image around for a few days then purge it. As far as what get's backed up and given to a customer that's a bit different.
I won't put client data on an external drive and give it to them unless they pay for it and I always explain that once it's in their hands if some damage occurs I can't be held responsible. Since I rarely take cold call clients that's worked well for me. For my residential clients, most of whom are also business clients, I try to get them to use Carbonite to backup their pictures, documents, email, etc and have had no problems with recovering data that way. I've created image backups of business client system in the past, but I don't really keep too many images like that around due to the vast amount of space you'd need and ultimately that's on your dime. I've created workstation images and put them on the clients server before to make recovery a bit simpler.
I've tinkered with and deployed in a limited role
Fog Server for making imaging, offline virus and memory tests easier. It just requires setting the computer to use BOOTP in the bios, and when booted will bring up a small windows with a selection of what you want to do. It can run MEMTEST or CLAMAV or even create a disk image without having to boot in to windows.
