If you mean gambling online yourself, it is generally not illegal to gamble with your own money, though conceivably you risk losing money if a site shuts down. I would note that most BTC gambling businesses that do any substantial volume, like SatoshiDice, have moved operations out of the country.
A site that operates overseas and takes BTC deposits directly and cashes out only to BTC is not subject to the main tool federal prosecutors have at their disposal, the Unlawful Internet Gambling Enforcement Act, which directly targets financial institutions. That's a big mallet, but with no banks to go after, this law is inapplicable to BTC.
However, I wouldn't place much faith in the argument that BTC is immune to state laws criminalizing gambling, which generally define gambling for the purposes of enforcement as wagering for "anything of value." If you can sell it for real money, buy goods or services with it, and it actually has a measurable market value, that's going to count as gambling. It might not count as "illegal gambling," especially if the house is getting no cut, but the moment you start raking and making money, it's probably covered.
So I'd say running a BTC gambling site in the physical United States is a pretty dicey proposition, though whether anything actually comes of it is dependent on whether some ambitious LEA actually feels like doing something about it. I'm not sure what monetary threshold would be big enough that anyone bothers, or whether they are even interested in BTC at the moment. The feds have shown little understanding of the concept so far.
I think it is highly probable that before any widespread enforcement effort, the FBI or whatever other LEA wants to do something will start making public statements indicating their intent to do, and that people will have some time to exit the market, perhaps safely, but it could be that they start with a bang by busting one of the major operators.
If you're planning on doing anything substantial, you should consider getting real legal advice, not just ask people on the Internet. Depending where you live, your local authorities may have a practice of doing little or nothing in this area, or they might be very aggressive.
This is bang on 100% the best advice so far.
I would also like to mention that one of the tools the government used against the online poker sites in the black Friday cases in the "the travel act" (IIRC). Online gaming in the USA is a cluster fuck ATM good luck doing something like this legally.
Question for you, why are there no real large AMERICAN online gambling sites/companies... if it was possible someone would be doing it legally now, not sure how you think you could somehow figure it out? You are also involving your friends, do you all understand what you are doing?