For Jean Csvihinka, 48, who works at a bank in Milford, getting a civil union meant paying tax on an additional $6,000 a year. Ms. Csvihinka said that adding her partner, Gina Bonfietti, 43, a self-employed piano technician, to her health insurance obligated her to pay a federal tax on the value of the additional coverage that married couples would not owe, and that since the civil union she has also had to pay tax on her daughters’ coverage even though the girls were on her plan, tax-free, before. She said she was told that “it’s a systems issue.”

Experts blame some of these problems on the disconnect between state taxes, which civil union couples can file jointly, and federal taxes, which they cannot because of the 1996 Defense of Marriage Act that defines marriage as between a man and a woman. Some employers provide people in same-sex partnerships with two W-2 forms, one that includes the imputed income for the extra health-care coverage for federal purposes and one that does not.

Maureen M. Murphy, a New Haven lawyer who has represented same-sex couples for 15 years, said it often takes civil union couples two or three times as long to prepare their taxes, because they need to fill out a dummy joint federal return in order to calculate figures they need for their Connecticut joint filing. “Believe me, we’ve run all-day continuing legal education seminars on this,” Ms. Murphy said.

One pair of plaintiffs in the case before the Supreme Court, Janet Peck and Carol Conklin, refused to get a civil union because, as Ms. Peck put it, they give “gays and lesbians an impossible choice between those rights that everybody needs and our own self-respect and dignity.” On a more practical level, the couple complained to the court that not being able to marry could jeopardize their “priority seats and access” to University of Connecticut women’s basketball games, among the most coveted rights or benefits a state resident might seek. Ms. Peck’s name is on the tickets, and should she die, the university allows them to be passed only to a spouse. Mike Enright, a spokesman for the university’s athletic program, said the Huskies “follow current state regulations,” suggesting that if the couple obtained a civil union they could transfer the tickets.

Amy Pear, a 39-year-old police captain in Middletown, said she was reminded again this month of her own murky legal status when she returned home from an overseas trip with June Lockert, 46, her better half for the last 14 years.

Arriving at Kennedy International Airport, the couple were asked whether they were one household. Captain Pear said she explained that they were, in Connecticut, because of their civil union. She said the customs officer sent them back to be processed separately since the federal government took a different view, and remarked “Welcome home” as she passed.

Captain Pear said she has also been unable to get a firm answer from Middletown officials as to whether Ms. Lockert would get survivor benefits if she died in the line of duty. “Unfortunately, a lot of people don’t know how civil unions will work because it’s not marriage,” Captain Pear said. “You ask does this apply or not, and they say maybe.”