If you are purposing JPEGs to the internet for people to view the images on their uncalibrated and unprofiled displays, the safest way of keeping the images having any semblance of how you intend they should look is to embed sRGB colour space and make sure that Black Point Compensation is selected.
Mark, if you are converting between working RGB spaces, where black is L*0, black point compensation does not make any difference to the result when its checked. It is ok to leave it unchecked then.