Not "getting the words right" cost a couple dearly, as a recent article in the Journal of Accountancy illustrated.
(What, you can't find your copy? Okay, I'll tell you what it said.)
In a recent Tax Court case (Durden, T.C. Memo 2012-140), a couple's $22,000 deduction for contributions to their church was disallowed, because they did not receive a "contemporaneous" written acknowledgement stating that "no goods or services were received" in exchange for their contributions.
The Code and Regulations require "contemporaneous" written acknowledgements for contributions of $250 or more. "Contemporaneous" in this case means the taxpayer must have the statement - with the proper language included - in their possession by the time the tax return is filed. You can't correct it "after the fact."
The moral of this story is: check your acknowledgements to make sure the required language is there.
If it isn't, get a corrected acknowledgement before you file your return.