OK, I'll chime in here. I am known to one-hand a saw, especially out of a bucket, but also in various instances while climbing. When I am one-handing, (like when I'm topping bradford pears---HA) it is at the front of my thoughts, and I sometimes act out the cut before I start the saw to help me visualize the eventual path of the bar.
Now, to push this in a different direction. If you wouldn't use a chainsaw one-handed, why in the world would you use a handsaw one-handed? Especially with the new silky saws and the like, you can cut through your rope or your body every bit as fast as with a chainsaw (possibly even faster on a loaded rope, a zubat with a new blade practically falls through a loaded rope!) I guess the body cuts are cleaner and easier to stitch up than a chainsaw cut, but what consolation is that? We were talking about this last week in safety meeting, and we are all just as afraid of a sharp handsaw as a chainsaw. Should we be 2-handing our handsaws? I don't think so, but I bet some do.