While it will take time for specific government regulations to come from the IRS and the Department of Labor, there are some items that are already very clear, according to Vanguard.

• Same-sex spouses who live in a state that recognizes their marriage will now have spousal consent rights, such as default beneficiary rights, qualified joint and survivor annuity benefits, and qualified preretirement survivor annuity benefits. They also will be able to request a qualified domestic relations order to protect their retirement benefits in the event of divorce.

• Same-sex spouses can now qualify for the more favorable required minimum distribution and rollover rules for retirement plans and IRAs that apply to spouses, rather than those for non-spouse beneficiaries.

• The IRS safe harbor for hardship distributions from a 401(k) plan will now apply to same-sex spouses, thus allowing qualifying distributions to pay for medical care, tuition and burial costs.

None of this is true in states that don't yet recognize same-sex marriages. 

By Aug. 1, 14 states, including the District of Columbia, will have allowed same-sex marriages. Many other states permit civil unions. However — and this is an important distinction — these federal benefits only apply to legally married couples, not those in civil unions. It's possible the laws pertaining to civil unions will evolve, but at this point the Supreme Court ruling doesn't cover them.

Still, "for those who live in a state where same-sex marriage is recognized and who are married, there are a number of things open to them," said Doug Rothermich, vice president wealth planning strategies TIAA-CREF. "This now automatically affords same-sex couples an array of retirement and estate planning tools that heterosexual couples have long enjoyed."

Of course, with these benefits come shared responsibilities, such as joint responsibility for spousal debt, not to mention the division of assets in the case of divorce.

Other issues are a bit more muddled — especially as they relate to ERISA plans. If an employee works in a state different from his residence, and the marriage laws conflict, it's not entirely clear which rules will apply to work-related benefits such as health insurance or retirement plan rights.

For example, take an Arizona company with some California employees. Arizona is a state without marriage equality, but California is. Will California-based employees be able to put their spouses on the company health and retirement plans? How will income earned from the Arizona company apply to a joint income tax filed by a California same-sex couple?

These questions have yet to be answered.

"That's an area where we need guidance from the agencies to help clients and plan sponsors," said Ronald Triche, assistant general counsel at the American Society of Pension Professionals and Actuaries. "Until we get guidance from the IRS and the Department of Labor about how this will be implemented, it's hard to move forward in some areas."

No guidance will be needed in two of the most important U.S. retirement programs – Social Security and Medicare, both of which will now be extended to married, same-sex couples.

The survivor and spousal benefits of these programs are significant, but under DOMA, they weren't available to married same-sex couples.

Social Security's survivor rules permit widows or widowers to receive up to 100 percent of a deceased spouse's benefit or his/her own benefit, whichever is greater. And a spouse can receive up to half of a living spouse's benefit, if it's larger than his or her own.

The rules even apply to divorced spouses in certain situations. Likewise, if a worker is eligible for Social Security disability benefits, a spouse or divorced spouse may qualify for up to 50 percent of the disabled worker's benefit amount.

The DOMA ruling also will open up valuable Medicare benefits to some married same-sex couples. Medicare eligibility is based on the number of quarters in which you have paid payroll taxes into the system. At age 65, anyone with a work history of at least 40 quarters can enroll for Medicare Part A (hospitalization) without paying a premium. Everyone pays a premium for Part B (doctors' visits), Part D (prescription drugs) or a supplemental Medical policy. Access to the entire program is predicated on Part A enrollment.

However, married spouses can enroll without paying a premium even if they don't have the requisite quarters of work history – another benefit that now will be available to same-sex couples.

What's that worth? Seniors without adequate work credits can buy into the system by paying a Part A premium out of pocket. This year, the monthly Part A premium is $243 for beneficiaries with 30 to 39 quarters of work history, and $441 for those with less than 30 quarters in the system.