Currently on Kubuntu 11.04. Now, any resolution below 1920x1080 displays perfectly. However, when I go to 1920x1080, the colors suddenly wash out, the brightness goes through the roof, all sorts of things go wonky with the display... I had this problem before, apparently managed to get it to fix itself via something simple like changing resolutions and going back, but I just picked up an HDMI AV receiver and am now routing the cable through it for the 7.1 audio. Audio works great, went in and swapped my receiver back to direct passthrough on that input, but sure enough, the video problem has returned, and persists when I plug the computer directly into the display. Anyone have any idea why I'm having issues only on that particular resolution, and why it would be something that has proven to be fixable (even if only via luck) in the past?

Try lowering the refresh rate at 1920x1080. It's about all you can do.

Dims the display overall, like someone enabled energy saving mode. Doesn't fix anything else.

You may have reached hardware limits.
lowering the refresh lowers the vertical frequency, which lowers the horizontal frequency. If you are determined to run 1920x and everything says it can do that, you'll need to cobble up an interlaced mode. This also lowers horizontal frequency, which is actually the problem.

In xorg.conf.d, you can set the following parameters
HorizSync 31.5-85
VertRefresh 50-120

1920x1080 will (wild guess) be about 2300x1200 when you allow for unseen bits of the frame. Do the sums. At 70Hz that would be 2300x1200x70 for a dot clock (193Mhz) and 1200x70 (=84Khz)for horizontal frequency. If you haven't an idea, set those figures I have above, and reduce the HorizSync by 10 each try(80,70,60 etc). When you get proper behaviour, try upping it by 5.

Hrm. Any idea why this is something that worked fine before -without- any special adjustments though?

I'll bet you changed distribution.

No, I unplugged the cable, plugged it into my receiver, plugged my receiver into my monitor, and it changed. It's now this way even when plugged directly into my monitor. It's the same exact problem I had happen before. My distro hasn't changed.