I bought the same 47" LG 3DTV that is being sold here about a year ago. I'm very happy with it, but I also only use the 3D for gaming. I have yet to watch a single movie in 3D and I'm not sure that I even want to.
One common complaint about passive 3D is that your 1080p TV becomes two interlaced 540p images. One eye sees every other horizontal line, so they each see 540 of them. That said, when actually using the 3D, you don't notice this at all. Well, unless you're reading small text, then you'll see the difference, but even then the total image that you see looks better in 3D than it does in 2D, simply because it has perceived depth.
If you're watching a movie in 3D, then you'll want to go with a really big TV (relative to the size of the room or your distance from it). This is because of how movies are filmed and the expectation that they're being viewed on a big movie theater screen. But when you're playing a game, the action is usually centered around a main character or item in the center of the screen and the depth is created around them, so a more "modest" 47 inch TV should be fine.