British Lawmakers Approve Gay Marriage

[milo]

"Couples who have a civil union will not have any of the protections or responsibilities federal law provides to married couples. These include social security survivors’ and spousal benefits, federal veterans’ spousal benefits, immigration rights associated with marriage, federal spousal employment benefits, the right to file joint federal tax returns, exemptions from income tax on your partner’s health benefits, the federal exemption from inheritance tax, and many other federal protections which are denied same-sex couples whether legally joined in a civil union or a civil marriage.
Also, most other states will not recognize the legal status of your civil union, even though they would recognize the Illinois marriage of a different-sex couple. This means that when you travel or if you move to another state or country, your union may not be recognized. As a result, you should considering taking certain precautions before you travel, such as executing health care and financial powers of attorney and carrying those with you.
Finally, the most important difference between civil unions and marriage for many individuals is the second-class nature of civil unions. Civil marriage is a widely recognized and respected social structure for two people who have committed to build their life together. Civil unions are not universally understood. It is unclear whether they will be given the same level of respect as marriage in Illinois and elsewhere. What is already clear is that different-sex couples get to choose whether to enter a civil marriage or a civil union; lesbian and gay male couples are given only the civil union option."

From the ACLU

That is both dated and from a biased source as I'm sure you know.