Once I switched to 1.4.3 pre-release, I noticed a bit of flickering in the room I had been in since 1.4 pre-release. It gets pretty noticeable once you see it.

HOW TO RECREATE:
(1) Light a room that contains chests, torches, glowstone, netherbrick, stone, and smooth sandstone.(These are the materials that were used to make the room)
(2) Stand still and look around (mostly in the corners)

This was in the vanilla multiplayer minecraft_server.jar provided at mojang.com.

I also noticed this in 1.4.2 when using a popular mod called "optifine" (while using certain texture packs). Maybe there are similar problems?

I cannot post a picture because it is a quick flicker, and I am too lazy to make a video

Thanks for the great game Mojang!