I also have my laptop on my lap, and I'm surfing Tribe.
(Don't ask why, but trust me that there's a good logical reason for this.)
At one point I find something on Tribe that I want to show to a coworker, so I cut the URL and then tried to paste it into the IM window.
It took me a bit to figure out why I couldn't get the cursor to move over to the other computer.
This is almost as good as the time that I was going crazy trying to drag-and-drop a post-it note from my monitor.