In the State of Oregon, and many other states, domestic partners must include employer contributions towards benefits as taxable income. This is not true for same sex partners or married couples, which is as it should be. But these protections from federal and state taxes on this "income" are not applicable toward opposite-sex domestic partners and are a significant financial consideration when negotiating the realm of health care (a world which is already unnecessarily complicated and expensive).
http://www.pcc.edu/hr/benefits/domestic-partner.html
http://www.hrc.org/resources/taxation-of-domestic-partner-benefits