I received a 1099-G form in the mail, I have never been unemployed or filed for unemployment benefits. How do I get to the bottom of this ? Is that the only reason I'd receive that ?

Who issued it?

A 1099G is a statement of taxable income issued by a government agency. So you must have received income from some government entity. Maybe a state tax refund.

Form 1099-G. Certain Government Payments.
Unemployment compensation (box 1), report the payment on Form 1040, line 19.
State or local income tax refunds, credits, or offsets (box 2), this amount is reported as income only if you itemized your deduction in 2008 and claimed deduction for these taxes. Use worksheet for Form 1040, line 10 and report on line 10.
ATAA payments (b0x 5), report on Form 1040, line 21.
Taxable grants (box 6), report on Form 1040, line 21, or on schedule C, C-EZ, E, or F or Form 4835.
Agricultural payments (box 7) and Market Gain (box 9) , report on schedule F.

Form 1099-G is also used to report your state tax refund for 2010.

If you itemized in 2010 and claimed the withheld state income taxes as a deduction, the refund is considered taxable income.