users of the starcraft forums say that this is a real problem, and that they hate it with a passion, "you should report them for cheating, and then explain in the report why you report them (easier for the guys that check reports).
As long as people who encounter those players do that, they will be banned eventually, sadly most people believe Blizzard doesn't care and thus they do not report these players, and thus they don't get banned. Nice vicious circle."