I really started to notice it when I moved from Indiana (UTC -5) to California (UTC -8). The threads and comment scoring seem very different depending on what time zone you are in.
From the East coast, in the morning, you pick up the late UK threads and comments, and at night the late afternoon California threads. From the West coast though, in the morning you catch the East coast threads (already in full swing), and at night, things die down a bit before the few Asia posts start to pickup (I stay up late).
It's strange how one site can have a few different feels based on who happens to be awake in the world.