Just because no one is really chiming in yet with a good answer I'm going to throw this out:


In the publishing world, it is advantageous to have you BW images reproduced in CMYK so that the blacks are richer and have more depth.


I'm pretty sure an ink jet will still try to print a grayscale image with all inks unless you select "black ink only" and if memory serves me, I recall that black by itself kind of has a yellow hue (maybe not an issue with high end printers).


So I'm going with leave them RGB.