Well, what happened to you demonstrates real needs to always have a current verified disk image just in case. Not only do you save a lot of time, you don't lose all your files either.
I'm in agreement that some sort of release notes or history should be provided at each update.
I have been running disk imaging software even longer than the 13 years of running avast and it has saved my bacon on many occasions. But I use it for what some would consider trivial things, if whatever the problem is if it is likely to take longer than restoring the image, then I restore my last weekly image. In this case the last disk image was only 1
1/
2 days before.
However, in this case I did a lot of hunting and trying to gather information for avast in the hope it might help others, hours and not minutes as the restore image took.
It almost took longer to boot into the CDs recovery environment once in I just restored the C drive and that took just under 5 minutes.
I think comprehensive update notes are the way to go (not highlights), whilst most people won't look at them, many will.