It's not so much when Bitcoin will hit $100, but when $100 is only worth 1 BTC.
I disagree strongly: the bitcoin economy is nowhere near the breadth or maturity of the USD economy. If it was, then we could talk coherently about the value of the dollar denominated in bitcoin. However, as it is now and for the near-term future, bitcoin's value is primarily determined by its exchange rate against the dollar, euro, or other currencies. If there was anything close to parity between the amounts of goods and services available for e.g. USD or EUR and bitcoin, then we could say something like '$100 is only worth 1 BTC', but not until then.
During this phase of bitcoin development, the gap between a speculative digital commodity and a full-fledged distributed digital economy needs to be bridged. As long as bitcoin is more accurately described as a digital commodity, it's more coherent to say that the price of bitcoin fluctuates against the dollar than the other way around.
All that being said, it be pretty sweet if we ever get to the point where we can talk about USD losing value against the bitcoin, but we won't be there until BTCUSD is at least $10,000. And there's a real chance that won't ever happen.
As to the topic post. I think bitcoin will pass $100 within the next two years, I'd put my guess around August 2013.
