NBC's (and other network's to a lesser extent) problem is that they don't stay consistent.
You have a favorite show, then suddenly it's moved to a different day or time or it's gone for two weeks, then back for one, then gone for another two weeks. It used to be that each show was on the same time every week, and all shows went on hiatus at the same time. The lack of consistency loses ratings, because people get tired of trying to find their show, then trying to figure out if it's a new one or repeat, especially if the show is so new that it doesn't have a solid fanbase yet.
This whole, "Catch the series premiere of Go On this Wednesday @7! Then catch it at its regular time on Thursday @ 8!" doesn't work in a show's favor. The Office has been so successful because they stuck with it and it's been on at the same time on Thursday since it started. The same with with their other successes like Seinfeld, Fraser, ER, and Friends. They all stuck with it at the same time, except for Fraser's last year.
Shows used to take up to three seasons to find their groove and fanbase, and they used to get that long. Now they only have three episodes. In today's television standards, Seinfeld would have been canceled in the middle of its first season.