I have found that there are a lot of npc's in the world who will not sleep. In Oblivion just about everyone went to sleep all at the same time. Except for the guards and inn keepers.

Who doesn't sleep?

Innkeepers.

Guards did sleep.... if you went in the barracks you would see them sleeping. There is a dayshift and a nightshift. Note: The best time to loot a castle was in a shift change because there would be a 30 second gap where guards wouldn't be at their posts. The worst time to get caught was also in the shift change... twice as many guards.

Most innkeepers also had a small cot behind the counter and would sleep for a few hours each night.

It is annoying that so many don't sleep in Skyrim. Actually I don't think any of the drunkards who hang out at the tavern in whiterun sleep.

"My favorite drinking buddy! Let's grab a pint!"

They have very irregular sleeping patterns. Belethor wouldn't sleep for like 2 nights in a row once.

They're watching...

Mass insomnia running rampit through Skyrim. Could it have something to do with the dragons? Let's ask the graybeards...........

Actually , I think some people are too nervous to actually sleep , especially innkeepers as thieves could rob them in such times.

It's funny, but the best time for me to loot houses is during the day. Noone is home.