Not YC but Tech Wildcatters (April-July): I hail from India holding a business visa and depending on airports, I generally don't have a problem staying 3-6 months (my I94 always gets 6 months of stamp). SFO and DFW immigration has been very welcoming to entrepreneurs. Can't say the same for ORD. The officer didn't know what a startup meant and thought I was making up a word; oh, and also apparently stealing jobs :/ Although I've only landed there just once and it could've been a one off case.

Strictly speaking, B1/B2 doesn't allow you to work. I have a visa called B1 in lieu of H which allows you to do H work without taking a salary, of course. It's also not tied to a particular company but to an individual. I have no idea how I got this visa because I applied for a regular B1 and the annotation was added to the visa – it also isn't a widely recognized visa (embassy issues it) and I would suggest against applying for it. I guess they gave it considering my history of startups.