The digital scoundrels at CheatHappens.com have posted an interesting article about what they're calling an "unprecedented act" from Blizzard. Namely, at the beginning of this month Blizzard began banning the Battlenet accounts and CD keys of StarCraft II players who were using cheats and trainers (at least one of which was created and distributed by CheatHappens.com) in their single player campaigns and in matches against the AI.
Blizzard's stance is that since those single player games affect the achievements and score displayed in multiplayer, they can't be standing for it. In response, CheatHappens point out that these elements "have no bearing on multiplayer standings, matches or games". Personally, I always thought achievements were harmless. This is causing me to reconsider.