peachy3333 did this last year. See this thread. NB, US Airways has given a 250% bonus in the past, as per this thread.
Double bonus for purchased miles (Another round: Feb-March 2010) - FlyerTalk Forums
30% bonus for transferred miles (from SPG, etc), according to this thread.
Also consider buying miles from AA, if you want to fly on Oneworld. 55k AA for 1000 USD, which is also 5.5% of Lifetime Gold (OW Sapphire).
Oh, and the reason that these airlines are doing this, is that they need more cash:
S&P's Most Likely to Default in 2010 List - DailyFinance
AMR = American Airlines
LCC = US Airways
UAL = United Airlines