A combination of factors makes the bitcoin currency very crash resistant.
A crash would occur under a mass sell out. Considering a very
significant event that undermines the security of the bitcoin system would have to occur for a mass sell out to be rationally justifiable, such as a government or other powerful group/individual spends massive resources to break the system, a hacking or some form of take down on mtgox occurs that involves many losing their bitcoins, or some entity creates a quantum computer capable of breaking the SHA256 encryption in reasonable time and starts targeting bitcoin accounts, I think it's safe to say with a very high probability (at least at the current state of events) that a mass sell out would occur due to snowballing speculation/panic selling combined with or initiated by large investors getting their bitcoins out.
Such a mass sellout will happen from time to time due to natural market movements. However any massively significant
crash, such as going from 30$/bitcoin to <1$/bitcoin or even <5$/bitcoin is very unlikely because of one thing... the community.
In order for the bitcoin to crest and crash the market would have to be overtaken by speculative investors. And by overtaken I mean a significant majority of all bitcoins must lay in the hands of these speculative investors. Only then will the sell rate be unsustainable and have no buyers to keep up with it. However, due to the bitcoin architecture, the strongest currently are early adopters. Many of these people have a vested interest not in just making a quick buck, but to see the bitcoin be adopted globally. At the current moment, with these people in control, the bitcoin will not crash. There isn't enough market initiative sufficient to make it crash.
This means we have NOT REACHED the start of a bitcoin bubble as of yet. It will happen, as the bitcoin gets more popular, and the balance of power shifts over to more powerful investors, that market activity will get even more extreme than is now. But whether or not that balance of power shift that would allow a massively significant crash to occur... could even occur, is debatable.
The graph on http://buttcoin.org/im-going-to-post-this-update-so-you-can-follow-along-at-home
is actually pretty accurate. The thing is the "mean" for the "return to the mean" phase has not been reached, and you can help that mean be as high as possible by doing the following.
WHAT YOU CAN DO:
1) For people with large vested interests in bitcoins: you should be aware that you have a lot of power on the market. Be aware of what you do, as any large actions could come back to bite you in the ass. But also be aware certain large actions could be necessary to save your investment.
2) For businesses: make using bitcoins to purchase things attractive. You could aim for simply breaking even or even selling at a slight loss based on the current market value of the bitcoin. Because there is potential for the bitcoin to rise in value significantly, you would be simultaneously offering customers prices that can't be beat, but also making a large profit as bitcoins rise in value. The only way this is sustainable is because bitcoin customers are growing exponentially. The bitcoin is increasing in value due to its inherent ponzi-scheme-esque exponential growth values. The only difference is that at the end (when the bitcoin is largely accepted and exponential growth becomes unsustainable) instead of a crash, the value stabilizes.
3) For everyone: you don't need to have a single bitcent in your account for the purpose of hoarding to do this. Simply when you need to buy something, see if it's for sale using bitcoins. Then buy however many bitcoins you need and spend it on that item. If buisnesses follow what I suggested above, it would be the best deal your money could buy anyways! Or separate your investment account from your account for spending power. I think hoarding is a very proper thing to do at the moment, but realize if you spend bitcoins (even if you just buy them and spend them immediately), you're helping raise the eventual "mean" that is referenced in the above graph. The bitcoin is a potentially very profitable environment for dealers, as you can sell a $10 item now and a month later, with raised bitcoin prices, have effectively sold that item for $20,$40,$100 or more. By buying items you're raising demand for buisness, and by raising demand for buisness, you're helping the bitcoin become globally accepted.