Not that i've noticed anyway, but as has been said, a tiny bit on the "inside" of a cotton ball, and get under the string so there is dry cotton between it and the board. If you want to be doubly safe, you could use a strip of plastic or electrical tape around the cotton too, so that there will certainly be no Spirit in contact with the fret-board. If your guitar is super expensive, or you just want to be doubly sure you could either talk to the company that made it or a professional luthier about it. Surgical Spirit evaporates almost immediately anyway, so its not like anything is being soaked into the wood. As for your previous question, I have found that it helps to keep the zing in the strings for longer, and it helps to keep the strings clean.