How big is my potato
It says something about the software development world that the answer to the comment
"How many people, I speculated, lacked scales in their kitchen but did have a computer close to hand."
is perhaps 'enough to justify this project.' I've lived with enough geeks to believe this to be true. However I've generally made a point of ensuring that at least one person in every house I've lived in was very serious about their home cooking, so scales have been in plentiful supply (although the PCs to scales ratio was typically 5+) . Still, there's a website for measuring potatos - take a look http://www.howbigismypotato.com
Perhaps more interesting than the site (fascinating as it is) is the blog, which gives a pretty good description of a project developed in iterations. Until I get round to having one of our internal projects set up so we can view each separate iteration I might use this for explaining to internal clients what 'not doing it all at once' actually looks like.