Even if you're in a completely darkened room all day, you know if it's AM/PM. The clue is that you're asleep for about 8 hours a day. You know when you wake up. AM/PM is useful for setting watch alarms, though.
I wore a watch for about 15 years straight, starting in 3rd grade. But now it just seems pointless. My cell phone, which is always with me, has a clock on it. So does my Ipod and my Pocket PC. My car has a clock in it. Every single room in my house has at least one clock in it. I'm in front of a computer for most of the day, which has a clock on it. I'm surrounded by clocks so why would I wear a watch, other than as a fashion accessory. I usually dress like a bum, so not having a watch is the least of my fashion worries.
Anyone here read Gizmodo? I've been a subscriber for 6 months now and they are obsessed with weird watches. There's some pretty crazy ones that they review. Here's a link to them all:
http://gizmodo.com/gadgets/watches/