When I feel like being a wiseass, I say "a lot" when asked. People usually push for a number, though 8D
Most of the time I just answer honestly. I've had some great conversations about fitness, weight loss, etc. just from my loss getting mentioned at some point.
I wasn't always comfortable doing that though, so I used to just say: "oh..I don't weigh myself." You people all know that is a BIG GIANT LIE since I was a daily weigher...