Nice experiment. A couple bug reports: The Tip button doesn't work in IE. And, I found TechCrunch on the list of the sites twice!!! One with www. and one without it.
I have actually witnessed it first hand. When I have a budget for advertising, I tend to use it up quickly; but when I don't, I spend a lot of time thinking of ideas to get free promotion in other ways. Lack of resources does push you to be more innovative. The only downside is if you find your fundded competitor spending on marketing and getting all the buzz and attention while no one ever talks about you.
Release as early as possible, but not too early to have something usable.It's okay to trim features, but it's not okay to release something buggy or unusable.
Wouldn't this be better built as a Facebook app? Just because users already have profiles there and won't need to signup for a new service. Just a thought.
The puzzle states that he has to be 100% sure that everyone had been to the room. "fairly confidently" is not good enough here. And, it won't matter if you increase the number of visits in a row to 5, 20, or more, there is still no guarantee.