Technically on a business tourist visa (forgotten what it is called, but if you are from the right country you just tick a box on your way in) I think you are allowed to attend meetings and tradeshows. From an IT perspective I am pretty sure you are able to do analysis if the aim is then go back to your home country and do development. But I cannot see how a startup can go there and actively start a business (although I guess you could argue it is similar to sitting around a pool on holiday checking a blackberry - big argument, but there is a case there - it isn't like you are an employee of anyone there).
Entering the US is always a bit painful, but I think when you come from a country that they don't have a major overstayer problem with then you are probably OK.
I'd be interested in how people from countries that don't qualify for visa waiver get on.