Earlier this year I took the Platinum Challenge as I wound up 20 nights short at the end of 2003. I had to stay 12 nights within a 60 day period or 18 nights within a 90 day period and then I was back to Platinum for the rest of the year. ^ Call the Platinum line after Jan. 1 and ask for the Platinum Challenge!
If you remain a gold, as the previous posted indicated you will lose the 48 hour guarantee and your bonus goes from 30% to 25%. However, you will get access to the Conceirge lounge, but you will probably never see an upgrade. Upgrades have been very, very rare for me as a platinum over the last 3 years.
Good Luck.