Great writeup. Very informative, speaking as someone new to the realm.

It seems it's only applicable to business models that rely on getting revenue directly from customers (i.e. buying subscriptions or widgets). Do you have any thoughts about how you might test an idea where your service is free, but you get revenue through advertising to your users? It would still be very valuable to get some sense of how useful users would find your site, how often they'd visit, etc..., but you don't really have a strong test (i.e. will they pay?)