(If you havent heard of bitcoin, its a currency of sorts, but not linked to any country or government. About as close as you can get to cash that you can email.)
I quite like the idea of it, even if in practice it may have a few flaws or teething troubles, I think in general it could work. It certainly makes buying and selling on-line easy as pie and cheap, and arguably safer. Also I would dearly love to see it kill of PayPal etc as the defacto online payment method.
I never paid much attention to it though until recently (which i regret, but hey). It's value has been steadily climbing, until the other day when there was a spike in buyers & price, then a market panic induced low. The reason for the panic was down to a lack of capacity at the main trading exchange, mtgox, which froze up due to the spike. They are back now though, and the market seems to be mostly back to normal now, albeit at a price back down now to something like the price it was before the spike at the end of last week.
At this point, I'm tempted to invest a bit of money in. I can visualise the price doing something like this:

Although bitcoin has the potential to replace cash, i dont see that happening for quite some time. I see it as a market similar to the gold market, where the currency is worth basically what people will pay you for it rather than its actual usefulness. The main difference I see is that the gold market is tried and tested - established and stable. There may be more opportunities for making money playing the (wildly) fluctuating market price of bitcoin.
Playing the markets aside though, my thinking is that (apart from some unforseen disaster like the US government sticking a legal oar in), bitcoin may be a decent longer term investment.
In my opinion, the cause of the recent spike seems to mainly be down to interest in the fledgling currency, and things like cyprus happening. The reason for the crash seems to be mainly due to a technical issue at the main exchange, which I think if had not happened the price would have stayed high.
I don't see that the initial interest that caused the spike has peaked. I think as more people see the possibilities of bitcoin (even if as just an investment/gambling opportunity rather than for physical purchases) the price will continue to rise, and as more exchanges become established the stability (one exchange crapping out would not affect the entire market so much) will only improve. Certainly in the short term, there are probably quite a few people like me who are considering investing just to see what happens and pushing more capital into the market.
It could be that I am mistaken, and the effect of the spike/crash has not been fully dealt with yet and the price does something like this:

In this case, it would obviously be a less than ideal time to buy, it would take longer to reach the same point, but I still think it would eventually.
Anywhoo, I'm not talking putting my mortgage on this, I'm not stupid enough to gamble more than I can afford to loose should the worst happen and it all bottoms out like the Zimbabwean dollar. But if the price does just continue to rise for the next year or two, I would be kicking myself for not taking a punt.
Ok... I now open the floor for discussion!