We were at Universal last New Year's and plan to be there again this year, staying at PBH. Plenty to do on NY's eve, depending on what you are looking for, how old you are, and how old everyone in your party is.
Universal Studios had a live band and dj playing until around 11:30, when the announcer came on and told us all to make our way to the lagoon (doesn't matter where you are around the lagoon, every spot is good) when midnight there was a massive fireworks display and musical montage on the big globes in the middle of the lagoon - it was awesome... one word of advice, while the daytime was quite nice, it got really cold by midnight, we were in our Northface's and Uggs, and we are from Massachusetts where we are used to cold winter nights, but this took us totally by surprise, we were freezing!!
There are a couple of nightclubs at City Walk for the 21+ crowd, all of the restaurants do something (Hard Rock has a special show I think). The real fun of the night was heading back on the boat ferry with all the drunks - it was comical.
Our kids were 15 and 16 and we had a great time.
Hope this helps!