If you are a registered domestic partner in a community property state (Nevada, California or Washington) the IRS now requires you to split your community income on your 2010 Federal returns. You have the option to amend your returns back to 2007 (depending on what year you became domestic partners).
For Nevada registered domestic partners, your registration can only date back to October 2009 when the Nevada Domestic Partner registry went into effect. However, if you were registered in another state prior to October 2009 you may still want to amend your prior returns. April 15, 2011 is the last day to amend 2007 for most couples so it is important to speak to your accountant regarding these matters as soon as possible.
Beware, if you use software and not a professional to do your taxes it is not beleived that anyone has developed software to deal with this nuance at this time. There is the right tool for every job and if you are a domestic partner in one of these three states then an accountant is the right tool for you.