Good ones. Here's a few I've gotten at the DC Metro:

1. As I was about to unfold my bike, I felt eyes upon me. I turn and two 8-10yr old kids are watching me.
me: you like my bike?
girl: yeah!
me: it's really handy for the Metro. ( I proceed to unfold bike as they watch)
boy: Man, I really can sure see how handy that thing is!

2. In the elevator, with my bike already folded up: a woman looks at my bike, looks at me, looks back at my bike, then says: How does it do that?

3. The one I get most often: How much does that thing weigh?