I don't understand what it is. I texture the inside of my level boundary brushes, sometimes with shaders, sometimes with ordinary textures, and then when I compile it and play the level, the backgrounds blur and bleed as I move around.

What is up?

EDIT: Oh yeah, my map is pretty big and it seems like the backgrounds blur and bleed as I move away from them, and they're fine close up. DOes map size matter?

Try setting in worldspawn:
"distancecull" "32768"
or some other high value, if you have maps with a LARGE open space that then this value should be larger than the distance between the furthest two points in that area. You may have to set "_blocksize" in worldspawn to higher values too to reduce vis data.