So you have received a free (cattle class?) flight by a guy you never met in real life but know from the Internets.
You are a software developer who made significant contributions to Bitcoin, a crypto currency used by people who want to escape the fiat currency and who are interested in privacy and don't like the government monetary policies. Let's not forget money laundering and illegal gambling. Let's not mention Silk Road and controlled substances legislation (I guess sports people in .au must be big fans of SR)

The company who invites you (Butterfly Labs Inc. - Bitcoin Mining Hardware - ASIC Bitcoin Miner) to come over is paying for your flight and your hotel. Do you already know what hotel you are staying in, immigration will ask. The said company is release a spiffing new piece of crypto hardware they hope to export out of the USA. They want you to write various articles to promote the product by endorsing it's existence and perhaps add some more software support.

Surely this is not a vacation trip but something a bit harder to explain to immigration. I see plenty of red flags going up, starting with the fact they paid for your trip (and they know that before you get onto the plane), you work in the field they are active in and you'll probably travel with the tools of your trade like a laptop.