Muggles on Broomsticks
I don't remember this being mentioned in canon or in the Lexicon but I was wondering if Muggles could ride brooms? It's been kind of nagging at me for a while because the conversation comes up in my story [though I doubt I'll actually have them going on brooms, that could be a recipe for disaster] and I was curious to see what everyone thought.
It's been my understanding that most magical objects, e.g. wands, broomsticks, ingredients for potions, etc. may work for Muggles, but they require that magical connection to work well. The primary example would be wands, as JKR has said before (I'll try to come back later with some links) that while a Muggle can pick up a wand and wave it around and maybe accidentally shoot a few (possibly dangerous) sparks of magic from it, the wand has to connect with the magic inside a person in order to carry out magical tasks. She says that the wand is a "vessel" for the wizard or witch's magic, so it's not so much the actual wand that's doing the work as it is the wizard/witch's born ability.
I think the same would go for broomsticks. A broomstick is an enchanted object, and if a non-magical person were to get on and try to fly, I think you are precisely right in saying it would be a "recipe for disaster." I just don't believe things would work right. There would be no magical connection, so that the broom's inanimate magic would be working freely with no human magical control. Does that make any sense?
In short, my personal opinion is that no, a Muggle would not be able to ride a broomstick - without being seriously injured or killed, or resulting in the serious injury or death of someone else.