CALIFORNIA STATUTES CLEARLY IDENTIFY NINE REAL DIFFERENCES BETWEEN MARRIAGE AND DOMESTIC PARTNERSHIPS
Finally, after noticing that many people are finding my blog looking for the "nine real differences between marriage and domestic partnerships", and lamenting that I could not supply the answer, I did some digging, and turned up this document (you have to download the rather large pdf from a link). I quote from foot note #241 in italics below.
Nine differences have been identified:
(1) common residence requirement for domestic partners, not applicable to spouses,
In other words, a married couple does not have to live together, but domestic partners do.
(2) application for lifting of the minimum age requirement not possible for domestic partners,
In other words, you can get married under a certain age with (I'm guessing) permission from your parents, but not become a DP.
(3) to register a domestic partnership the couple must file adeclaration with the Secretary of State, whilst spouses must obtain a marriage licence from the county clerk,
So DPs deal with a different part of the government, somewhat higher up.
(4) possibility for confidential marriage in which marriage certificate and date of the marriage are not made public, not applicable to domestic partners,
Marriages can legally be made secret, DPs cannot.
(5) summary dissolution for domestic partnership initiated by filing joint notice of termination with Secretary of State, for summary dissolution of a marriage is petitioned to the superior court,
Similar to the third point.
(6) residency requirements for dissolution are different providing for a forum necessitates for domestic partners,
I'm not sure what the Latin term means, but from what I've read, if a DP moves out of state, the partnership is dissolved; this may be what is referred to here.
(7) differences with respect to the State Public Employee’s Retirement System,
I don't know what this refers to, but I'd guess DPs don't get pension benefits the same way as spouses.
(8) difference in interpretation with regards the property tax exemption for unmarried spouse of a veteran and
(9) putative spouse doctrine does not apply to domestic partners.
I don't know what this means, but a Google search seems to show that this difference no longer applies.
Make of this list what you will; I only offer it as information.