There are a LOT of ASICs preordered that more or less will show up and begin hashing. The 200TH (formerly 100TH) project is coming online fully, a number of other mines are coming on, and I fully expect the difficulty will shoot past 1B, which is where the early Avalon miners stop being profitable. People will continue ordering hardware well past the point it's worth running, IMO.
The other factor which affects profitability is the price of BTC, which at $140 today is 12 times the price it was in January. I personally started looking into all of this in May and saw BTC drop to $68 and then rebound. And its increasing steadily.
I've been reading other threads that are predicting the value of BTC will continue to increase at the 10x to 12x per year. I have a hard time believing that will continue much longer, but even a 5x to 6x increase next year will put the price of BTC at $700 to $800 each. If that occurs it will keep me mining even if I can only get a BTC every 3 months at my fastest mining rate.
But, that being said, I want to get as many BTC now as I can, and 10 to 20 block erupters will generate 1 to 2 BTC every month for the short term.