You are out on a local ride with a few friends, stop for coffee, and somebody asks you (or you ask him) "care to swap bikes for the next ___?"
I've done this twice: 1) I asked - and was granted the privilege - of swapping my K75 for an R1200R. Though I never had ridden an oilhead, I wasn't surprised by the strong response to the throttle. But I was surprised by the lack of a gear indicator on this much newer bike and the vibration just above 4000 rpm. "They all do that." Hmmm. Since my swappee was a former K75 owner, I didn't have any fears for my bike in his hands. We rode this curvy road at moderate speeds and nothing bad happened, and I learned that his bike was not the bike of my dreams. 2) A guy asked me if I would swap my K100RS for his G650 (?) We hadn't gone far before I knew that was another bike not for me. He thought my K100 would get him far to many speeding tickets. Another lesson learned, and again no bad consequences.
I'm sure you have all felt the temptation to ride a very different bike from your current ride, whether that is an old airhead, the latest high hp offering from BMW, a Ducati, etc. You also know this short-term swap will not involve any parking lot practice to get acquainted with the brakes, response to handle bar inputs, etc. There are certainly some dangers.
So what do you do, and why?