Some people in the comments of my blog have hinted that I should have just "followed the rules" and nothing would have happened. This is incorrect -- I did follow the rules. It is perfectly legal for an independent contractor to be contracted to perform a task in the US, come in, do it, and leave. That is (amongst other things) what the "business" checkbox on the I94W is for.
What landed me in this trouble is that the immigration agent decided that even though I am CEO of a company in Germany and have no employment contract with Blackhat (just a contract as an independent contractor), that the status of "independent contractor" does not apply to me - his interpretation was that I was an "employee" of Blackhat without an H1B visa.
This is not a case of me screwing up my paperwork. This is a case of an immigration agent that did not understand my attempts at explaining that I am not a Blackhat employee, and me not knowing the subtleties of being interviewed by DHS/INS agents.
I hope I will be able to clarify the misunderstanding on Thursday morning at the consulate.
Small addition to clarify: It is perfectly legitimate to come to the US to hold lectures and trainings of the kind that I am holding at Blackhat. To reiterate: The problem originated solely from a misunderstanding where it was presumed I was an "employee" of a US company, which is not correct.