If you're referring to the gift tax exclusion ($12,000 per individual or $24,000 per couple in 2008), 529 college savings plans do allow for five-year gift tax averaging, where you can spread the contribution over the next five years for gift tax purposes (meaning that the total for the five years cannot exceed $60,000 or $120,000, respectively). See IRC Section 529(c)(2)(B).

CanItBe,
If you're talking about tax deductions for 529 plan contributions, I'm assuming you're talking about a STATE income tax deduction, since you don't receive a tax deduction at the Federal level for 529 plan contributions.

Thus, without knowing what state you are in, it is difficult to answer this question for certain.

But generally speaking, for every state of which I'm aware, if you exceed the maximum tax deduction for the current year, you may potentially be able to carry the excess amount forward and deduct it in a future year. However, I'm not aware of any states where you are able to carry it back to prior years if you underutilized in the past.

So if you're contributing more than the maximum for this year, you should check your state's laws to see if at least you can carry forward the excess to use as a deduction in the future. But that's likely the best you'll be able to get, if your state allows it.

I hope that helps a little!