Facinating question...
FYI: This thread is a comprehensive collection of BW info and techniques, but does not address "What's your favorite method?" nor grain:
http://www.retouchpro.com/forums/pho...yscale-bw.html
Early on I used channel mixer, but seldom do anymore now that I have CS3, which has a spectacular BW adjustment layer. That (now) is my first tool of choice because it's so dang easy and there is more control than using Channel Mixer.
More times than not, however, I use a combination of the color channels copied as separate layers and combined using layer masks and blend modes. This method affords maximum control over the outcome because of its flexibility. The L layer (from a Lab version of the image) is used as a background. On top of that are layers whose sources are the R, G, B channels.
There are MANY
convert color to BW actions at
www.AtnCentral.com that simplify the layer setup.
Grain-wise, when I use it, I use the same method as you (layer set to Overlay [rarely Hard or Soft Light], filled with 50% grey, add noise to taste, adjust layer opacity). From most viewing distances, I don't really see the point though. Most people these days have never seen a traditional BW print (from film and printed in a lab), so IMO there's little to gain by adding simulated grain for this audience. I might add a little grain to disguise shadow areas to which digital noise reduction was applied.