Final answer:
A taxpayer who made their final 2008 state estimated tax payment on January 15, 2009, should report it on their 2008 tax return, which would potentially affect their tax refund.
Step-by-step explanation:
When a taxpayer makes their final state estimated tax payment on January 15, 2009, for the tax year 2008, it should be reported on their tax return for the year 2008. This payment is treated as made during the tax year for which the estimated taxes are being calculated, even though the actual payment date is in the following calendar year.
The payment would typically be included on Form 1040 or a similar tax form used to file state income taxes, under estimated taxes paid or withholding. It's important to maintain accurate records of all estimated tax payments when filing because they contribute to the total tax payments made during the year and can affect whether the taxpayer owes more or is eligible for a tax refund.