To open or contribute to an HSA you must meet certain eligibility requirements. Specifically:

You must be covered by a qualified high deductible health plan on the first day of the month
You cannot be covered by any other health plan that is not a qualified high deductible health plan, including spouse’s health insurance
You cannot be covered [...]

In reviewing the 1018-page House Bill on health reform there appear to be a few issues that could negatively impact health savings accounts. There is a limit on the out-of-pocket costs that could effectively narrow the plan design for HSAs. The limits set in the bill set a max-out-of pockets (single/family) of  $5,000 and $10,000. There [...]

HSA contributions are based on your insurance coverage and age. For 2009 the limits are:

Single accounts (only one person covereed on the health insurance policy)—$3,000.00
Family accounts ( multiple people covereed on the health insurance policy)—$5,950.00
Additional contribution for account holders who attain age 55 by December 31, 2009—$1,000.00

Contribution tips:
 You have until April 15 to finalize your [...]

In Administrative, Procedural, and Miscellaneous Notice 2004-50, the IRS addresses this question. See Questions 2 and 4, excerpted below:
 Q-2. May an otherwise eligible individual who is eligible for Medicare, but not enrolled in Medicare Part A or Part B, contribute to an HSA?
 A-2. Yes. Section 223(b)(7) states that an individual ceases to be an eligible individual [...]

Some of our account holders have asked about the security of their HSA money invested in the Vanguard Prime Money Market Fund. Vanguard has issued a statement confirming their continued participation in the Treasury Guarantee Program. You can get details by following the link below:
Vanguard money market funds participate in extension of Treasury Guarantee Program