It doubled from 200 to 400 in one week, why couldn't it do the same once it reaches 500 here shortly? Think logarithmic.

Definitively possible, but logarithmic (exponential) growth cannot last forever in real world. It has to slow down and stop at some point.

The growth has been faster than exponential, though. If you look at 1-year charts, the growth appears to be exponential in the interval between Dec 2012 and Nov 2013. Then something happened in Nov 2013.

Nov, 2013

ATM dropped in Canada
BTC got popular in small pockets in China, then that is getting bigger and bigger and bigger (as they teach more and more of their young children how to get involved, and the schools allow for even more flow from child to child)
MCXnow dropped shares, and tons of people went in for that.
Over 10,000 messages were sent out by me alone to tell people about Altcoins and how companies can make their own, and I'm sure other people shared the links as well (either after opening a message from me, or just because they are good people and do that already). So probably upwards of 20,000 messages went out these past 2 weeks.

DO EVERYTHING YOU CAN TO HELP. IF YOU LIKE SEEING BITCOIN GO UP, DO SOMETHING TO KEEP IT THAT WAY!!!!