Alright guys. I am a computer guy, econ buff of the Austrian bent, etc.
In one sentence:
Bitcoins are a secure and anonymous internet currency backed by the processing power of the computers behind them.
Details:
How they are created:
Bitcoins are produced by people running software that "discovers" new coins. Each coin is basically an encryption key. The keys must be found by computers crunching numbers. You know how there is software that looks for new prime numbers? Think of it like that. There are thousands or tens of thousands of nerds out there using their computers to try to find bitcoins. Their computers are crunching numbers all day and night to discover new bitcoins - new passwords/keys that are secure within the bitcoin network.
How they are limited:
The peer to peer network is self aware to the extent that it understands the total money supply. It automatically throttles the production of bitcoins to limit bitcoin inflation. It is progressively more difficult for computers to find new bitcoins, just like how it becomes more and more difficult to find bigger prime numbers.
How they are "secure":
At no point is your name associated with bitcoins, just like CASH. Also, because you have no bank account (yet) to deposit these in, if your computer crashes, you lose your bitcoins if they were not backed up. Just like CASH. So when you hear senators complaining, they are just complaining about the same weaknesses that exist in CASH.
How they are backed:
Computers. Silver dollars were backed with silver. Under the gold standard, dollars were backed with gold. With bitcoins, the coins are literally backed by the computers that created them. Gold/silver dollars are the easiest comparison.
When gold dollars become very valuable, ie, when you can buy a lot with a gold dollar, gold miners ramp up production to produce more gold. Same deal with bitcoins. When bitcoins go up in value, more people dedicate their computers to find new bitcoins.
Fast forward 5, 10, 25 years from now. Why should google have acres of servers? There is plenty of idle computation power in the world today that if google could figure out how to harness it, they could offload all of that work onto the net.
Their very demand to utilize the combined computation power of the net (including your computer when you aren't using it) can potentially be the driving force of bitcoin value. If demand for computation pool power goes up, ie, google wants to add capacity dedicated to their software, they can pay in bitcoins. This would lead people to divert their resources from "mining" bitcoins to serving google's demand.
Bitcoins serve to commoditize computational power. One bitcoin will represent x number of computational time/production.
This creates a trade off for a "miner": mine/create more bitcoins (gold) or sell your computation time for other pursuits, such as to run google.
This leads to a currency backed by computation. If you compare gold to a computer, which is more useful?
As far as trading goes, here are the main risks:
1. Anyone with $10-20 million and know how could walk in and crush this market by dominating the production process. By the way, if anyone wants to do this, send me a message. I can help you monopolize the bitcoin production market.
2. It is very volatile right now. For better or worse, swings from $10 to $30 are commonplace within a couple days, sometimes intraday. You can't short (yet, mtgox is working on bitcoin margin so who knows?). You can only buy low and sell high. You can't sell high and buy low.
3. Also for better or worse, you can see a fair representation of the market depth at some exchanges. Some show you most of the limit orders. There is some ability to have shadow orders that are invisible. But you can still more or less get a feel for the market and predict how you can move the market far more than most other markets. Also given the limited size, it is within the ability of many here to move.
4. Some people have a shitload of bitcoins. One guy has like 297,000 bitcoins. At recent prices of ~$20 per coin, that is like $5,940,000 worth of bitcoins. If someone like that tries to cash in too quickly, they will destroy the market.