icebraining: decentralization and optional anonymity are key selling points of Bitcoin; without these two features, it looks a lot like existing payment systems.
I know, my point is that those selling points are irrelevant to the masses, because to take advantage of them you need to run the Bitcoin client and manage your own keys, which most people won't do. So they can't "lose" anything.
Now, as for why would you use a system like this instead of one based on conventional currencies, well, don't ask me!