2) Look at this image to see the difference between different brands and their size 8 measurements.
http://www.nytimes.com/imagepages/2011/04/24/business/201104... via http://thesocietypages.org/graphicsociology/tag/womens-size-...
There's many variables to sizing. It wouldn't be impossible to create a database of measurements for every single piece of clothing.
And then there's the issue of shrinkage.
Those are irrelevant details. The basic form of input is "person A gives rating R to item B". This is precisely the formulation behind successful solutions to the netflix problem.
What I find a little disappointing is that the top 3 prizes for this Netflix-Prize-style competition total $7,000 in value. Is technical brainpower, even that of students, really worth that little? Maybe startups should band together to hold their own optimization contests if the 'market rates' are so low.
People saying that size numbers vary greatly are missing the point. If I say a particular piece fits me well (regardless of its listed size) and then a bunch of other people say it fits them well (regardless of its listed size), the site can then aggregate the other pieces of clothing that those people said fit them well to show me clothes that potentially fit me well (regardless of their listed sizes).
I would just call it data analysis, not crowd-sourcing