For all you guys strapping a backpack or something similar to the pillion, a word of caution. I used to use a fanny pack strapped to the pillion to care a few necessities when riding (water, eppy pen, etc). One weekend in the twisties, we pulled into a restaurant for lunch and I smelled something like burning rags. In reality it was burning fanny pack and it's contents. Fortunately, it melted the water bottle which apparently put out the smoldering mess.
I guess that the bag slid back far enough on the seat that it drooped down over the right side exhaust pipe and started the process. In the end, the plastic piece that goes between the pipes melted away (I just have the top half now) and the heat was enough to blister the fake metal coating on the end of the right side pipe.
Could have been worse I guess, I could have been sitting in the restaurant and looked out the window to see the bike smoldering in a heap :Flash:
Just one last thing. For a couple months after this happened I could smell the faint aroma of melted plastic when idling at a traffic light. So I guess those who have the swirling gas theory have something there.