Please tell me this doesn't work with old MF lenses? Do this relies in the lens or the body?
I have been using MF lenses for 5 months now and haven't ever used or heard about this feature (or if I did, I never got to put further attention to it).
I use it all the time in the studio when I've got the camera set on manual mode- I'd guess at worst it'd require the AF-D coupling, which is independent of the screwdriver focus motor- but I wouldn't be surprised to see it work with any lens- I've never thought about it and have used it since the day I bought a new 8008s on my Nikon bodies. In fact, I find the left and right arrows to be totally useful in manual mode. All my lenses are AF-D or AF-S, so I can't try it out on anything else, it works in manual mode with either of those though. If I've got my modeling lights set to track the strobe power settings and it's all turned down, the dot and triangles are often a bit better than my eye in the dark. The triangles tell you which way to turn the focus ring and the green dot means it's in focus.
Let us know if it works on all-manual lenses- it's probably not as convenient as changing to a split prism focusing screen, but it's a lot cheaper!