[Guenter in Ontario]

For my $0.02 worth. I find a picture can be extremely useful to help me identify a part or location/orientation of that part in "how to" instructions.

I like the idea of the thumbnail, provided it is placed in the place where it is used to illustrate something being described. If I don't need the picture to help me, I can skip over the thumbnail. If I need that illustration, it helps to be able to enlarge it and see it in greater detail.