I can't really describe it other than random chunks around me will load but not properly, they will load like 10 blocks below or above, there can be floating gravel in rows, random items together like lava,levers,pumpkins, and mob spawners floating. The way I've found out how to get rid of these is to jump into it which then my character will freeze and I log out and log back in.
PS: I'm using minecraftforge-universal-1.4.6-6.5.0.467