The Internal Revenue Service released Rev. Proc. 2011-14 on January 10, 2011, a 325 page document explaining the rules for making "automatic" accounting changes.
Under the law, a taxpayer can't change its accounting method without consent (read "approval") from the IRS. But, there are a non-controversial changes for which the IRS will automatically grant consent if the taxpayer follows specific rules.
The changes are effective January 10,2011, for years ending on or after January 10, 2011. That's IRS speak for "immediately".
If you have the time, you can find a copy of Rev. Proc. 2011-14 on the IRS website, at http://www.irs.gov/pub/irs-drop/rp-11-14.pdf.