I got asked this yesterday, at a training I've been sent to for work. My response was that I'm a motorcyclist, and have tried invisibility: it sucks. (Basically, no one on the road can see you if you're on a motorcycle -- that would only get worse if I were ACTUALLY invisible, and wouldn't be restricted to times when I was riding). On the other hand, I've worked in and visited a lot of buildings with really bad elevators, so being able to bypass those and fly up seems like it would be awesome. Also, my knees are bad, and there are occasional days when going up stairs really sucks.

Neither one is really practical -- I'd rather be able to teleport, say -- but flight feels like it would have more practical uses to me.