When considering mining, be sure to take into account the increasing difficulty. Any hashing power you purchase now will be a smaller slice of the pie in a year, so a high discount rate, and/or decaying revenue can make the option much less attractive.
less important but still a factor .
when we did 20% every 2 weeks for about 1.5 years this was really true.
this will NEVER happen under current conditions.
In order for it to happen we need a chip to do 0.01 watts vs current best of .31 watts .
Another way for it to happen would be BTC price goes up up up this problem does raise the diff fast but since the coins go up you still make money.