each state gets to define the terms on its own. for example, NJ just passed one that is EVERYTHING marriage is, without the name "marriage". other states may decide to offer no acomodations, or to offer some things (wills and estates, health care proxies, etc).
Found this and it answers my question....
Although similar to marriage, a domestic partnership does not confer any of the 1,138 rights afforded to married couples by the federal government. Domestic partnerships in the United States are determined by each state or local jurisdiction, so there is no nationwide consistency on the rights, responsibilities, and benefits accorded domestic partners.
http://en.wikipedia.org/wiki/Domestic_partnerships_in_the_United_States