I mostly shoot RAW... I have been playing with some of the art filters, but I still find that my B&W conversion works much better...
I think the in camera monotone is just a zero saturation. The Grainy film filter adds contrast and noise to it.. However I have tried using the monotone color effect just to be able to see the shot in B&W in the EVF while composing.
I shoot RAW, then, if an image looks like a good BW candidate, in Lightroom run a one-click conversion (takes less than a second). If it looks OK then I go back to the original colour and convert within LR and or with the Silver Effex plugin.
I do raw only. It is my intention to do B&W. So if I make a color image, it was a new discovery for me. I don't see/like color.
Ok, there are many ways to convert to B&W but....
it all depends on how well your color image is.
I bring the image into LR, make it look as good as I can in a color image..then use Silver Effex either in LR or in PS.
The main difference between shooting color and converting to B&W vs shooting in-camera B&W is that converting from color gives you options in how individual colors are handled in the B&W conversion. Our cameras may give us a few "filters" to choose from, but it's nice to be able to make those decisions after the fact, plus there are more options that way. Lightroom lets you tweak each color. For example, in a single image I might assign aqua to a bright tone in order to have a bright tropical sea while assigning blue to a dark tone for a more dramatic sky, all the while previewing the effect of these changes on the conversion.
I shoot jpeg for B&W as the G1's Dynamic B&W is what I am looking for, that was the reason I bought the LX3, I was enthused that Panasonic had incorporated it into the G1.
I like that I don't have to spend time in P&P afterwards, sometimes I prefer that that the process has been taken out of my hands as I am never completely satisfied/convinced that my P&P is quite 'there' with B&W.
I always shoot Raw, convert using ACR in photoshop and once I am happy with the colour version I use Nik Silver Effex to convert to B&W, it is probably the best dedicated B&W conversion tool I have personally ever used and it embeds into Photoshop easily and smoothly.