[Arkady]

Just remember if you convert to CMYK, the gamut is narrower - pixels of the same colour are discarded and in the case of certain mid-greys are replaced with Process Black for print purposes.

DO NOT EVER convert back to RGB as all of the lost information is gone forever and the resulting images will look horrible. Might appear OK on the monitor, but Horrible, trust me - just had an afternoon with the Gurus from Adobe and my head's still reeling from all the info...

If I ever manage to make sense of any of it, I'll post up here - there was another good way of converting to Mono, which I'll try and get down ASAP.