Here's a trick I learned from a furniture refinisher....instead of a commercial tack rag treated with whatever that goo is, you can make your own using a wad of cheesecloth with a little bit of polyurethane varnish worked into it. That way anything that's left behind is a finishing material and not some sort of wax or whatever.
Keep the rag stored in a ziplock bag between uses and it doesn't dry out for a very long time.