Is it likely that we will interview soon?

I am a U.S. citizen living in New York who petitioned for my foreign national husband in September 2010. My husband arrived in the U.S. legally, overstayed his visa, and after we got married, I filed to adjust his status to permanent resident. I am just wondering how long this process takes. USCIC sent our receipts about a week after receiving the application (dated October 1, 2010). In November 2010, my husband received his biometrics appointment, and a few weeks after that, he received a work permit. In that time, he has gotten a social security number and a learner's permit. I always thought that the process took about 3-4 months. But it is the interview that we are waiting for at this point. Since December, we have not been receiving any information from USCIS and it's now been over 5 months since they acknowledged receipt of the application. Just a week ago, my husband got a letter stating he has been registered for Selective Service (he's 25) and I guess immigration did it on his behalf. Nevertheless, do you think our interview will be held soon??