I setup my LN40A650 TV yesterday, have 360, my other PC, PS2, and Wii hooked up to it. The quality is absolutely superb; the red ring that most people worry about is pretty much a no-factor, as you cannot see the red tone until you turn the TV off and be under direct lighting (the red tone doesn't glow). The glossy surface does attract a lot of dust, so make sure your room is clean.
The 360 looks really good on it, although I have it hooked up via VGA to achieve the 1920x1080 resolution (which doesn't support the 120Hz smooth motion with VGA input). Devil May Cry 4 looks very clean and crisp on it, no ghosting, no blurring, and lots of options to set the color just the way you want. The screen settings (such as brightness, backlit level, contrast, colors, ratio, 120Hz, black & white level, etc) are input specific, so you are free to set each device to your tasting without worrying about distorting settings of your other devices. But that's probably standard in most TVs nowadays.
To display my PC, I used a DVI to HDMI cable and it works nicely, although the TV doesn't recognize 16:10 resolutions (typical for widescreen LCD), any 16:9 runs fine. So if you plan on playing a game with the TV, make sure the resolution it is running at is supported by the game AND the TV, otherwise you'll be stuck with a black screen. I'm running my desktop resolution at its native 1920X1080; edge to edge it looks very crisp, each character I'm typing here are pixel fine when looked upclose at the TV. One problem I found out is that if I'm on a website that has red text, the redness tends to bleed one pixel to the right, almost like a shadowy image of the text. Only happens with red text though, red images look fine. So I might have to play around with the color settings some more.
The speakers from the TV works fine for regular TV programs, and maybe older games. But they're dinky compared to a stereo setup.
One con about this TV is the lack of rear Composite and S-Video input (they're both on the left side, and only 1 of each, which shares the same Red/White audio input) So if you have a couple of old devices (such as SNES and Dreamcast), you'll need to use an external A/V switch.
All in all, I'm extremely happy with the TV, it is definitely $1500+ well spent.