I was talking with a friend a few days ago and he said he was re-doing his taxes back to 2007. I'm kind of nerdly about tax rules, and I had not heard of this, so I assume that there may be others who have not either.
A May, 2010 IRS letter allows domestic partners in community property states to split income between the partners (who still have to file separately.) If one partner makes significantly more than the other, this has advantages because they then fall into a lower tax rate. He and his husband (married during the window before California Prop 8) have been domestic partners for many years, so they are allowed to restate their taxes back through 2007 (a three-year IRS window on re-filing for a refund.)
I haven't researched this, but there is apparently a time constraint of April 15th, 2011 for refiling some or all of the prior years (since my friend is rushing to get his 2007 re-done by then.)
IRS Chief Counsel Advisory 201021050: http://www.irs.gov/pub/irs-wd/1021048.pdf
Private Letter Ruling 201021048: http://www.irs.gov/pub/irs-wd/1021050.pdf
A 90 minute webinar from January 2011: http://www.ustream.tv/recorded/11982059