Medicare open enrollment this year is from October 15-December 7. This is for any change to your Part D drug plan or your Medicare Advantage plan (if you have one) which will then become effective on 01/01/12. You may have noticed an increase in advertisements for plans since the open enrollment dates were moved up this year.
Last year, a couple of the Part D drug plans decided to opt out of the Medicare program altogether. If you should receive a letter from your plan stating that they are doing that this year, you may choose another plan.