Considering that all bikes, even those that seem to be identical, have a noticably different feel, swapping bikes is a sure recipe for disaster. Along with a number of other statistics, a lot of crashes occure when riding a strange bike.
The OL and I will sometimes swap bikes because we both have a number of miles on all the ones we have.
It is a necessity for shop mechanics to take test rides.
There is an occasional dire emergency like the need to get a friends bike home after he has been incapacitated (or incarcerated).
Otherwise, it's just not done. It is a touchy thing just to allow someone else to sit on your bike or ask permission to sit on someones.
Demo bikes, renta-bikes, shop loaners, etc. are different, but still something to be wary of. You don't know how well they've been cared for and, there is the factor of having a bit of a strange feel.
In general, riding another persons bike is a lot like attending a service at a church of a different religion, it just seems wierd and doesn't feel quite the right thing to do.
According to legend,Sonny Barger once summed it up quite well. 'Love is the feeling you get when you like something as much as your motorcycle.'
