As somebody who participated in a Startup Weekend, I would say that these events definitely help to create startups. Launchrock, for example, came out of a Startup Weekend. It is hard to gauge the intensity level you will get out of your members after the weekend is completed.
Overall, I do think that Startup Weekends are great events, and I highly recommend that you attend them if you have a chance.
Still, whats the probability of random people meeting each other and creating ad-hoc teams. How realistic it sounds that this whole group (not a team yet) will form a real startup company and build a product for the next 2-5 years?
Without knowing this probability in absolute terms, I think it is safe to say it's higher than all of this happening _without_ these random people meeting. :)
I participated in the startup weekend in Des Moines two weekends ago. It was a great experience, sure most of the groups won't be going anywhere but it is a phenomenal networking opportunity and its a great way of learning more about skills that you may not have (in my case, I learned a lot about marketing).
http://portland.startupweekend.org/
Well document how it goes. Probably in video :>