Bitcoin, brilliant in design, sidesteps the need for most of this trust.
Bitcoin is a sort of digital gold with a built in transaction system. Awesome and very useful.
Bitcoin's base value comes from fanboys, folks willing to take a stand for their monetary ideology, but most importantly its usefulness in transactions that can't be done online for legal reasons or when a person would prefer not to reveal their identity. Due to this base value, it has attracted speculators who have driven up its price way beyond its value based on its base uses.
That said, in every day transactions, is it useful or practical for people to exchange their dollars (or other currency), pay 4% to move it to Bitinstant so they can get it into MTGOX, so that they can buy some Bitcoin (another 1/2 % fee), so that they can buy a pizza at their corner store? I'm going to go out on a limb and say "no."
This is the MAIN problem with Bitcoin. It is not useful as a transaction system to purchase every day items and does not fit well into the current system. Would you exchange your dollars for euros to buy a pizza in the USA? Then why would you do that with Bitcoin? You wouldn't unless you already had a bunch of Bitcoin or you were living your ideology.
Ripple on the other hand, is first and foremost a PAYMENT AND TRANSACTION SYSTEM. It can handle trust based transactions that people currently use and will therefore be readily accepted into everyday use (unlike Bitcoin).
So where does XRP and ripples (the currency in Ripple) fit in this equation?
I'm guessing but...
Opencoin, Inc., is smart in that they have printed up the currency in their instance of the pre-open source server almost like a stock issue. They have a certain number of shares that they are banking will increase in value, since xrp is the Bitcoin/gold in the Ripple system. They can hand out these "shares" like an IPO without the usual regulatory rigmorole and without having banks in between each transaction. Ingenious in my opinion. However, as mainly a transaction system, the value of the xrp will only increase and be worth something if Opencoin Inc. gains an early mover advantage in the market with their version of Ripple.
Anyone can make a Facebook clone even though Facebook isn't open source. The software isn't what makes Facebook worth something. It's the network of people and the infrastructure possible because of it. I think Opencoin is attempting to reach the critical mass needed to make sure that their instance of the server is looked at more favorably because of the network adoption vs. a clone.
If they succeed then their xrp will be worth quite a bit, in my opinion. If they don't they can still make money consulting with people running or implementing the software. The former would be preferable I would think.
So Ripple is taking the exact opposite approach of Bitcoin to gain adoption of xrp. Bitcoin people have to convince others to use Bitcoin in situations where they would normally use their regular currency. Ripple will merely need to get people to use their payment network for currencies they are already used to (by partnering with banks and other financial services) and xrp will become valuable as a result of that (it being the only trust-free currency in Ripple).