Folks have used some automotive products in the past with mild abrasives to polish out satin finishes to a gloss. Sometimes the results are great, other times flaws in the wood become more obvious.
Scratch-X, a compound with rapidly deteriorating abrasives is a readily-available one (Wal-Mart, etc.), but I've been told that recently they started putting silicone into the mixture. Silicone is bad for guitar repair because it is very difficult to get rid of and prevents adhesives from working properly if it actually gets on to the raw wood. I don't know how significant that is. I wouldn't worry if you're just doing the back of the guitar, say, since there's very little reason to think about repair of the exterior there.
I think there are other products that don't have silicone. "Fast-Cut" (or something like that) was bandied about on the Acoustic Guitar Forum as a great product for this.
Personally, I don't like satin on the back of a guitar because it makes noise when it shifts against your body. On the other hand, I very much *do* like a satin neck.
