I recently paid for some local tacos using Bitcoin. My friend who was unfamilar with Bitcoin thought it was strange, like I technically didn't pay for them or something. We got into discussing Bitcoin and one of the questions he asked me was:
"Why would you want Bitcoins instead of cash?". For a second I didn't know what to say; then I thought about it and here is what I came up with. Feel free to contribute to this.

1) More security (especially if you are careful).

2) Bitcoins are a potential investment, cash is not. Paper currency only really goes down in value, Bitcoins have a lot of potential to be worth more as time goes on.

3) Fast, worldwide transactions at your fingertips.

4) Similar to #3, but it's a universal currency. It's legal in most countries of the world and you don't need any kind of currency conversion to send money to people in a different country than your own.