New Jersey is one of a handful of states (Colorado, Hawaii, Illinois, Nevada and Oregon) which have purportedly granted equal treatment under the law to same-sex couples using a legal entity distinct from marriage. With the federal government now recognizing legal state same-sex marriages for various federal purposes like social security, income taxes and immigration you have the situation where states that intended to grant equal rights and responsibilities to same-sex couples as legally married opposite-sex couples legally can not do so unless they grant those couples access to federal benefits, which can only happen through a state-issued marriage. In fact, you have an even odder situation where a same-sex couple could go to a state and get married and go back to their home state (which does not recognize their marriage) and that couple would have more rights (due to federal law and public policy) than a same-sex couple in a civil union or registered domestic partnership.
The situation in New Jersey is actually pretty clear cut because the Supreme Court issued a ruling called Lewis v. Harris that ordered the state to treat same-sex couples and opposite-sex couples equally under state law, which led to the enactment of a civil union law. This context led a lower court judge to rule September 26th that marriages in New Jersey needed to begin October 21 and which is being appealed by Governor Chris Christie despite polls showing nearly two-thirds of the New Jersey public wants the state to stop preventing marriage equality from coming to the Garden State.
I expect the Court will agree to issue a stay on the lower court ruling until it makes a final determination in Garden State Equality v. Dow. Otherwise the Court would be allowing marriages to start occurring only to have them stop if they decide to overturn the lower court.
There's also other issues complicating New Jersey's path to marriage equality in 2013: there is a January 2013 deadline to override Christie's earlier veto of a marriage equality in the state Legislature, Christie is up for re-election this November and there are currently two vacancies on the 7-member state Supreme Court being filled temporarily by appellate court judges. Despite these complications, I expect that New Jersey will have marriage equality by this time next year.