Seems things are rallying too fast. Here are some reason why bitcoin could crash.
1. If you trade in bitcoins you still have to find a buyer of them if you want a pizza. Thus you will have to use a service to exchange your money to dollars on their terms. If you drive to a bitcoin meet-up you are still wasting gas to do the exchange. You will have a middleman more often.
2. There is a risk of lost, stolen, or disk failure wallets. Yes you can lose your wallet in real life, but you usually find it under the bed.
3. Shops are slow in adjusting prices, if the price rises and their store might have prices that are 2 months old and they seem expensive. What if prices crash 90% will the shop honor the price? I doubt it they buy all their materials in USD, CAD, RUB, or EUD.
4. There is no record of exchange. What if you buy a car and you go to pick it up and there is no car or address? You are out 10,000 BTC. If you buy something over the internet even for 1 BTC, if they don't send it you are out of luck.
5. The churning of your hard-drive is already annoying to run the bitcoin client. If the economy gets 10x bigger that churning is going to be 10x bigger. Are there any stats to Mb per day you waste on hard disk space? What about bandwidth?
6. In the end you might have to end up using a bitcoin bank anyways where you store your bitcoins to take the risk out of lost wallets. Then you run the risk that the goldsmiths, take your money and spend it loans and blow.
7. There is always the risk of someone destroying the network or finding a flaw and taking the system down. Since BTC could be used for money laundering, it might be a big goal of the governments of the world to take it down.
8. What if people stopped mining BTC, or the euphoria of a deflationary currency would people lose interest in it?
I suppose you say all these are already factored into the price of BTC.
"But guys! You can't live in that house! It doesn't even have a roof! How can you ever expect that to succeed! This is not going to work, guys! Stop working on it, you can't even live in it!"