The Netflix Tech Blog has this very interesting piece which is very insightful: http://techblog.netflix.com/2011/01/how-we-determine-product-success.html.
In particular, this point is very important although easily and often very voluntarily ignored by so many researchers:
There is a big lesson we’ve learned here, which is that the ideal execution of an idea can be twice as effective as a prototype, or maybe even more. But the ideal implementation is never ten times better than an artful prototype. Polish won’t turn a negative signal into a positive one. Often, the ideal execution is barely better than a good prototype, from a measurement perspective.