Just curious, did they need H1B visa (or other paperworks) for the first few months in the states?
I don't think so. I think you can come for a short time to the US with no problem. It's staying for years that's hard.
We love YC here in Canada.
SocialPicks is incorporated in Delaware. To attend YC's SFP '07, I applied for a 4-month TN Visa at a port of entry (Vancouver airport) en route to Cambridge. More info can be found at http://travel.state.gov/visa/temp/types/types_1274.html