I was going to say just about the same thing as spyderqueen (sans the actual grammatical reasoning, though I agree with it).

I dislike "cum" as a verb, as a description of action. I'd even say it puts me off. As a noun, I'm okay with either "cum" or "come."

Incidentally, the OED includes "to experience sexual orgasm" as a definition of the verb form of "come" and "semen ejaculated at sexual climax" as a definition of the noun form of "come." No such listings for "cum." Not that I think the OED should necessarily guide anyone in this instance--just thought it was interesting. :-)