Mellow, this is a very pertinent point. "Common law" marriages are common in Midwestern states, the former "frontier" states, as the niceties of formal marriage processes were more difficult to obtain at the time the laws were solidified. States that no longer recognize common law marriages are generally the ones that have codified the process - set them down in law, thus modifying the "common" law through "civil" law. California (and Washington State) are "community property" states - a civil law concept - which is often confused with "common law" but is completely different, and really has more to do with inheritance and such (the law of descent and distribution).
Your question, though, about States recognizing marriages of other States (including common law), is precisely on point. While the "Full faith and credit" clause of the U.S. Constitution (Article IV,Section 1 - which governs the rights and obligations of the States within the Union) provides,
Full faith and credit shall be given in each state to the public acts, records, and judicial proceedings of every other state. And the Congress may by general laws prescribe the manner in which such acts, records, and proceedings shall be proved, and the effect thereof.
States have generally been given more latitude in the area of "domestic" or "family" law. Most will recognize most marriages performed, or recognized, in other States, but anti-miscegenation laws, for example, were for a good deal of time - well over 100 years - considered constitutional. (Pace v. Alabama, 106 U.S. 583 (1883), was a case in which the United States Supreme Court affirmed that Alabama's anti-miscegenation statute was constitutional. This ruling was overturned by the Supreme Court in 1964 in McLaughlin v. Florida and in 1967 in Loving v. Virginia.) DoMA is a law that was passed by Congress in part to repudiate the requirements of Article IV, Section 1. I have always felt it was unconstitutional on that basis alone.
As more States recognize marriage equality, it will become harder and harder to maintain the distinction between those marriages - which, by the way, DO have the formality that common law marriages lack - and other forms, such as religious, civil, or common law. It is a matter of time... I am just anxious to see that it happens, and repeal of DoMA is a good (big) first step.
