Has anyone been stupid enough to try to break in?

I've heard some of those rumors too. The main problems I have with them is that Area 51 is the military base Groom Lake. I was in the military and I haven't been to a base where the guards are private security. The guards are armed and allowed to shoot intruders as they would be classified as a threat. I don't know if it's shoot to kill though.

Through my own logic, I would think that if someone made it to a certain point the guards would stop them, demand them to leave, and have someone make follow them to make sure they were leaving. If they didn't, they would either be shot (again, they would be classified as a threat) or arrested for trespassing. Since Groom Lake is a top secret base, if they are arrested, they would be subjected to a deep background check, interrogated for a long period of time, be forced to sign a contract indicated they aren't allowed to talk about what they did or what they saw, and then be sent to prison. If they happened to not go to prison, then I imagine they would be put on a list that the government will keep track of in a Big Brother sense.

Obviously, I could be wrong. I think I might actually try to research that now that you brought it up. =)

It's like you said, it would make them think about what they were doing with their lives.

A towel is about the most massively useful thing an interstellar hitchhiker can have.

For a while the policy, as I understand it, has been intercepting people who go past the boundary, a brief questioning, and usually a heavy fine of some sort ("trespassing"). I feel bad for the operator of a legit "area 51 tour" - he normally takes a small bus full of tourists right up to the point where everyone is still "legal," remains there for a moment and then turns back around. During one of his tours he got distracted somehow, and crossed the boundary, and was stopped, questioned and written up.
Makes sense - it's a fairly proportional response to people whose curiosity and courage end just a bit past the base's outer boundaries.
Now, if someone were to somehow evade the private security teams stationed outside, and get caught poking around... I doubt they would be summarily executed (unless presenting a real threat) or tortured, but they would probably be interrogated for quite some time. Someone able to get that far would have unusual skills and/or equipment to evade detection, and quite likely some sinister motives. I think at this point uniformed intelligence personnel would be asking the questions (not private security), trying to ferret out motive, how they succeeded, what (if any) plans they had for their furtive recon of the base, etc. Then they would probably be charged with felony level trespassing, and whatever else they can come up with.

...and Mrs. Taylor sure seems to use a lotta ice, whenever he's away