On exponential systems
It is hard to extrapolate what is going to happen from any set of data. One thing is for sure: in the real world, any simple model that shows a continuing increase will run into a real physical limit. And if it is an exponentially increasing curve that we are forecasting, that limit is going to come sooner rather than later.
For example, Moore's Law has defied this limiting for decades. If you think that means it will continue to do so for decades more, then don't invest on the stockmarket - you are a danger to yourself.
The only question is when. Oh, and what (is going to limit us).
[update 2013-04-09 See more on extrapolation]