Good explanations, Tim. Any other Flickr members on here want to chime in?
Garry, your What's In A Box pics are super-useful, especially as they deal with the klickies and accessories that are impossible to definitively list any other way; even with the original box in your hand, you can't see all the furniture inside a house, say. A lot of the parts you show don't have known numbers, but some do, and some are common enough that making a temporary number (to show that more than one set has it) has value. It's not exactly the focus of what I was talking about, but certainly goes along with it, and I think that making links, somehow, from them to the corresponding parts pages in the DB would be useful to visitors.
I think the thing about the fort, and the old Steck castles, is that it didn't much matter exactly you put it together. Not that your fort-pictures aren't useful: I'm going to link to the gallery from the sets, and you just watch your stats increase! System X, on the other hand, is pretty mesmerizing to someone buying a jumble of parts on ebay. They'd need just as much help or more, and when they get to a step using a part that isn't in their box, they need to know the number to order it, since it can, probably, be ordered. So, sure... no need to get grandiose at first: any information added is a good thing. Agreed?