Deflation seems to be happening at a tremendous pace (for a unit of exchange). So, that 21 million bitcoins will, if things continue, be "worth" dramatically more in the future. I suppose this is built-in to the system as a means to encourage early adopters.

But, given that there are very few means to cash out into other currencies, and the products one can buy with bitcoins are extremely limited and generally virtual goods, it's still wildly speculative that they have any longterm value.

Their low cash-value is probably almost wholly due the difficulty in getting cash for them.

Deflation of bitcoins can effectively be infinite, but should slow significantly if/when a significant amount of people get in on it and start using them.

I think it would be enough to jumpstart the process if one service that already reliably trades virtual currency for money (say, EVE) were to start accepting bitcoins for the purchase of said virtual currency.

Absolutely true. Which won't happen until the developers of a game such as Eve can use bitcoins for buying something more than phone cards and online poker chips. Developers need to eat.

bitcoins are divisible, and their value, like paper money, is asigned by those receiving them

Current prices are roughly 4 BTC per dollar, at www.mtgox.com. This is the only functioning USD-BTC exchange.

If you can buy them for 221/USD somewhere, buy a lot. You will be happily selling them for USD within the day.

So how many bitcoins are currently in existence? What is the value of every bitcoin that exists right now?

http://www.bitcoinwatch.com/

  4.87 million BTC
  or 1031762 USD
  or 21339945 RUB
  or 1047 ounces of gold

Based on relatively low transaction volumes, but you get the idea.