Yeah, that mineral spirits trick is a lifesaver. I did the same thing on some oak cabinets a while back. Wiping it down shows you exactly how the wood will look when the stain hits it, all the hidden spots that will suck up more color. It lets you spot those trouble areas so you can sand them out more before you even open the can. Really saves you from a nasty surprise after all the work is done. It's one of those simple steps that makes all the difference.