J.G.
I will ask the woman who does our DCFSA when she gets in and hopefully remember to repost. So far as I know about DCFSA it cannot be used retro. In other words if you did not declare it for 2009 you cannot take it. Meh, I will look it up on checkpoint. I do know the only tax credit you can take in 2010 for 2009 is IRA contributions so I am pretty sure you can't take 2009.
The IRS deems it an insurance contract so you cannot take the exemption for 2009 unless it was already declared and funded through a qualified program. So far as 2010 goes if you have not funded it through a qualified program and you do not see using it then don't. The problem comes in if you do need it later on in the year. Unless there is a qualifing event you will not be able to enter the plan mid year. I do not have a list of the qualifying events.
The tax consequences are easy. It is an exemption, in other words any money placed into a DCFSA is exempt from your adjusted gross income. Your savings is only your marginal tax rate. This savings is also not realized until you file your tax returns in 2011.
I would not recomend trying to trick the system and claiming it in 2009. DCFSA is reported on a W-2 and is very easy for the IRS to verify. You will be audited well maybe not will but you have a very high chance.
Without looking it up, and I don't have the time, I am pretty sure there is a deduction for child care expenses. If you paid child care expenses in 2009 they can be deducted. If you are wondering the difference and exemption like DCFSA is for AGI, a deduction is from AGI and subject to floors and ceilings. In other words deductions are pennies on the dollar.
Have fun!