Government will move in on Bitcoin in 12-18months from now
Until then the price of BTC will go up as more services are developed for it and use increases, due to its natural competitive advantage over PayPal and other online money services
The bloodshed will then start.
First, MtGox will be shut down; their bank account will be frozen and their business & owner in Japan seized
All other bank accounts involved in exchanging Bitcoins will be frozen & similar fates will occur to their proprieters
At that point demand for BTC will be reduced because of reduced liquidity
12-18 of growth at the present rate will mean it's too late for governments to stop it.
The demand for exchanges will be lower because people will actually spend their coins rather than just trade them for other currencies. You won't need an online exchange because everybody will know someone who will give them cash for Bitcoins and vice versa.