Question about deducting a matching contribution on your tax return; does it make a difference what year you deduct the contribution for as long as you do not double dip?

If you make a contribution designated for the 2006 plan year in 2007 (you make the contribution before the tax return comes due for the 2006 tax year), but decided to deduct this contribution for the 2007 tax return, would they allow this? Does it matter just as long as a taxpayer does not double dip (i.e., take that contribution as a deduction for both years)?

Yes, these could be deducted for either year, assuming all other requirements for deductibility are met.

The "default" under IRC 404 is that they are deductible in the fiscal year when paid. 404(a)(6) provides the special dispensation that you mentioned, to deduct for the prior year, as long as you meet the requirements.