You should file the return as soon as possible. Since you have a refund, IRS is not likely to impose the late filing penalty. Your refund will be forfeited if you do not file and claim it within 3 years of the original due date.
IRS can possibly hold your 2009 refund if you do not file. This is due to the fact that IRS shows income with a reduction for single filing status and 1 exemption until you file the return and give them your other facts. This is not likely, but has been suggested to IRS to generate more income for IRS and to encourage compliance from taxpayers.