I hope it is a problem in their script of the site , i don't think they would steal ( for theirs reputations sake ). I hope it is not a hack, lets watch our blocks at block explorer and see what happens :S
Oh! I'm not sure of my address. I tried the one that I sent to back when I was trying to mine bitcoins, but it does not have registered my last few transactions, so it must have switched addresses on me or something :/
Check your mail , Mybitcoin robot always sends mails about transactions , from these mails you can know your address
I never gave them my email! when I signed up I was never asked for one and I never remember seeing anything that would let me do so. I wasn't worried at the time, but now I feel very foolish!