You cannot predict this correctly.
There is no way..

The only way to predict its value is to know what will happen in the feature in our society.

For instance:
Will Tradehill get hacked?
Will some rich guy invest a million dollars?
Will some early adopter sell half a million Bitcoins and get the whole market screwed up.
Will a nasty major trojan infect thousands of people and get there wallet stolen.
Will Bruce his tv ad hit mainstream?
Will Bitcoin hit CNN?
Will Greece adopt Bitcoin as there curreny?

Etcetera...


There is no way to predict this.
Its all depended of major events wich will get Bitcoin negative or positve publicity.
I do no understand why people base there predictions on past grow rate.