Google TV is the biggest change to Android TV we've seen in years, and although it may well have its drawbacks, it sounds like it's pretty good at serving you the content you actually want. It also has an easily accessible watchlist that you can add movies and shows from various services. We now know that this list is also integrated with the watchlist feature in Google Search, as well as the wishlist in the Play Store.
Adding a TV show or movie to your Google watchlist is as easy as searching for it and then hitting a button, and on Google TV itself, each listing also has this feature. The new Google TV app, formerly Play Movies & TV, is no different. There's also a completely separate wishlist in your Google Play Store account that you might suppose is reserved for apps and games, but it's now an integrated list of everything (see below).
Google Search, Play Movies & TV (soon to be just Google TV), and Play Store.
This might be a little confusing to begin with, especially if your Play Store wishlist gets clogged up with things you don't expect to be there, but it will certainly make tracking Google TV content a whole lot easier. And that's really the point of the new Google TV interface, seemingly, to make the TV-watching experience as frictionless as possible. For more on how well it achieves that goal, check out Ryan's review.