Square just recently announced that they will be releasing a Final Fantasy XIII trailer in 2007. While I couldn't be more excited for the game, I have to admit that I'm a bit indifferent to getting my hands on it. For me at a player, at least, demos are often an unnecessary thing.
Don't get me wrong, getting to trial a game before you decide to buy it is an all-too-rare opportunity, short of waiting for a generous friend to buy it first. From the developer's point of view, too, releasing a demo or beta is an opportunity (for those on-schedule enough to make it happen) to get some consumer feedback before the final version is released. Frankly, though, there are just some games that I am going to buy -- Smash Brothers Brawl, FFXIII, and Halo 3 being some strong examples. Even though I will have read pretty much every piece of info out there for these games, I'd still rather experience them fresh. I had the FFXII demo in-hand when I bought Dragon Quest VIII, and never popped it in (which probably says a lot for DQ VIII, as well).
Demos are fantastic for the industry, and serve a lot better as a teaser than trailers do, but in some cases, I just don't need it. I'm sold. Thanks though, Square.