My husband's AOS interview was on 1/16/2008 in Dallas. When the interview was over and he was told that he had been approved, the IO handed him a letter with the regulations required for all LPR's.
Concerning leaving the US, this letter states:
"Any trips out of the United States where you leave and don't come back at all for one year are not permitted. You will lose your permanent residence status in the United States and could be turned away at the port of entry into the United States. Any trips out of the United States where you are gone for six months without returning can affect a future application for citizenship. If U.S. citizenship is something that you are interested in, you should limit any trips to less than six months while you are in permanent resident status."