I've been using Fast Fret for about 9 or 10 years now, and it has had no adverse effect on any of my guitar necks, fretboards, or bodies, and it DOES brighten the strings for another couple of sets' playing.
In Earl Scruggs' banjo book, he mentioned that he ran the fingers of his fretting hand through his brilliantined hair before going on stage, to facilitate smoother playing.
If I had hair, I'd be out looking for brilliantine.

Seamus