I said I'd never use such things... BUT having had my custom ACG for nearly a year now, I do miss fret markers. Especially when playing on a neutral neck and playing a lot of chordal pieces towards the bottom end of the neck.
I recently invested in some faux abalone fret markers made from some kind of 0.07mm thick wizard material. They look OK, they feel OK, they do absolutely serve the purpose of seeing where I'm at, but I'm still not convinced. Being a hard core stickler for originality, in pains me that these are on the bass, but they are definitely useful!
Naturally I've applied them in the same position Alan tends to place his luminlay, just to make it feel slightly more like they've always been there!