This is taken from Louis LaPointe (http://www.lubedev.com/smartgas/quickies.htm):
"MYTH: Overfilling your crankcase with oil can cause engine damage.
HINT: It is perfectly okay to overfill your engine by one quart of oil. Your engine will love you for it. Especially at higher RPM. The oil level is not level when the engine is running. Plus the "level" keeps getting lower and lower as you rev the engine at high speeds. If fact if you drive fast enough, the engine will suck air instead of oil. Your engine will blow its guts all over the pavement because the oil at high speed hangs in the rocker covers and does not easily return to the oil pan."
What happens to the engine when a crankcase IS overfilled? How does an engine behave if it's been overfilled?