By the way, I would like to say that plastic welding done RIGHT, can indeed provide a good repair, but you can't just take any old piece of tie wrap you have laying around and melt it into any piece of plastic and expect good results. The key to plastic welding is to identify the type of plastic being used and match the welding rod to it.
This is why ABS cement works so well on ABS plastic. It is the proper adhesive that is matched to the type of plastic you are trying to repair. ABS cement won't work at all on polyethylene, polypropylene, polystyrene, or polyvinyl chloride. But it works great on ABS, which is what most (but not all) motorcycle fairing parts are made of.
Here is a good link to a site that has some good info on plastic welding. You'll notice that one of the first things they tell you is that the KEY to plastic welding is to identifying the type of material and matching the welding rod to it.
http://www.plasticweldingandtools.com/