Major Nelson: don't share accounts or cheat at Gamerscore
Major Nelson also lays down a warning to anyone using artificial means to increase their Gamerscore. He notes that such accounts may have their gamerscore removed altogether and any achievements earned on such an account will not be able to be reacquired. And, as you might expect, such an account (and the console on which it resides) could also be banned from Xbox Live entirely.
We're not sure what prompted the warning (an increase in one or both activities perhaps), but we're sure it's good advice. Besides, what's the point of cheating to get Gamerscore? Where's the fun in that? Remember kids, if you cheat to inflate your Gamerscore, you're no better than a pro athlete.