If you are giving a product or service away I don’t think you can assert that you have “product/market fit.” You have a very compelling application, but until you figure out who is going to pay you for it, and how much it’s worth to them, I don’t think you can put a check in the box next to “product/market fit” since you don’t pass this test from the same Marc Andreessen post you reference ( http://blog.pmarca.com/2007/06/the-pmarca-gu-2.html ):
And you can always feel product/market fit when it’s happening. The customers are buying the product just as fast as you can make it — or usage is growing just as fast as you can add more servers. Money from customers is piling up in your company checking account.
Well, revenue is a beautiful thing, certainly. You can define product/market fit however you like-- but by that definition, most consumer apps don't have it. A customer can "buy" a product with money or their time/attention. I'd say both YouTube and Facebook have found a great product/market fit. And Gmail. Andreessen found a great product/market fit with the Netscape browser, but monetization of it really only came in the form of a few bizdev deals (which didn't cover costs, I don't think). Money, in many of these iconic companies, was NOT piling up.
Regarding my company, we focused initially on a non-paying market (individual lifehackers), as that was easiest to build for and launch a rough beta for. They "pay" in blog posts, tweets, word of mouth-- they've driven every single business lead we've gotten. Now we've got a new market (teams) that we have to find a "fit" for. Wish us luck!
And you can always feel product/market fit when it’s happening. The customers are buying the product just as fast as you can make it — or usage is growing just as fast as you can add more servers. Money from customers is piling up in your company checking account.