Man what a thread! I'm in the Chicago area where our temperature inversions are very high. The guitar sees all temperature and humidity combinations throughout a one year period. Let me tell you what I do. For customers, I see a lot of filthy grime and it needs to be removed. It is not good for the wood. I use Naptha (lighter fluid is ok), and sometimes if I really have to I will use Flax soap, or murphy's oil soap very sparingly with a toothbrush for major ground in ca ca. With the speed in which I do it, nothing is really getting below the surface. Maybe 1mil or so. *For mildly dirty fingerboards, I use lemon oil. But just enough to moisten the rag. I don't want it soaking in the board. Everything we're talking about is surface related. The problems are when you dump it on and it soaks into the grains. It can then TRAP moisture in, keep moisture out, do all sorts of things counterproductive. I don't like the Gibson stuff. It is really thin and it sucks waaaaay down into the pores. It also comes back up for a long time after you put it on. In my experience, it is addictive, because it is temporary and then it dries you fretboard out so that you need it more. *By the way all they did was go to a company that was already making it either for gun stocks or furniture or whatever and get their name on it. *As for maple, Glen is right on. *But I don't like any spray endust product on bare wood. There are fragrances and thinners and waxes and lots of other things in there that I don't want on my board. Also, if you have hands that gunk up a fretboard, anything you put on there, if it sticks in there, like linseed or tons of lemon oil, will become gunk later, and the process repeats. You do have to clean wood sometimes, too because if all you are doing is rubbing lemon oil in, you are mashing your gunk into the grains just by the rubbing you are doing. Man this is a long post. Maybe I'll make up a fretboard care sheet. Another reason we oil is to prevent cracking. Lemon oil does just fine. Drying of the wood also means shrinkage leading to cracking. The oil helps prevent this. As far as warping and frets pulling out, The expanding and contracting due to inversions really contributes. Oiling will cut down on that too. Re-cap: Kirk, the Gibson stuff dries the board as it evaporates, making you need it again. The lemon oil does not, unless it has alcohol or other thinners in it. Cowcowcow, you put too much on. Just a little on the rag is enough, and no waiting before you wipe it off. Do it instantly, removing as much as you can. *Tomizm, extra lemon oil slicking your strings will soak into them killing them sooner. The oil gets between the wrappings and the core, deadening the string. Madwell, keep doing what you're doing, making sure that if it's every two weeks, use very little and keep wiping it dry like you are doing. And Glen, a really dark, oily rosewood fretboard can be a sign of majorly clogged pores choking off the wood. Take the unoiled guitar, and then put a little lemon oil on the fretboard when you get it.