AAGH!!! I'm hyperventilating here. Petroleum products are terrible for vinyl! So are harsh solvents and cleaners. They'll dry out the vinyl, despite using protectants. Over time, they shorten the life of the material.
So, what does Glenn use? In a pinch, Fantastic. It's easy on vinyl and won't harm it. But usually you'll find me reaching for the 303 cleaners and protectants: http://www.303products.com/tech/index.cfm?fuseaction=feature.display&feature_id=18
Awesome stuff, easy to use, works better than anything you'll find in the automotive dept. They also make an excellent fiberglass protectant with UV protection that works on vinyl, plexiglass, and rubber too. No need to buy a bunch of different bottles for different surfaces on your boat.