I was wondering the same thing with my new premiere, which I got Thursday. No HD menus, no network connectivity (although it could connect to the TiVo service. I spoke to three different people before I got the right answer. The issue is on Tivo's end, not the box itself. When the tech looked at my account he said that several "groups" were missing that enable certain functionality. It's a known issue that started last week, and he put my name on a list to get a software update when it's fixed sometime next week.
Before he did that though, he gave me a procedure to try. First under the "System Information" screen, check to see what code is listed next to TivoToGo. If you haven't gone to TiVo.com to change the preferences yet, it should say i,i,i. Next go to Tivo.com, click on DVR preferences, an check both boxes. It will also help to rename the DVR to something recognizable.
Once you click save and get a confirmation, force the tivo to connect several times (it took me close to 15) until the code next to TiVoToGo is different. If it worked properly, the code should change to a,a,a and you should be good to go. If it didn't work, it should change to i,i,a and you'll have to call and have them place you on the list.