Don't get me wrong, I feel that it can really contribute to a great atmosphere; BUT I don't want them to overdo it. I want really beautiful sunsets and sunrises. Not all the time, but some of the time!
I want to be able to stare at the sunset/sunrise and say "Darn, that's really beautiful".
The North is known for having some really beautiful sunsets and sunrises. I know, I practically live there. And I hope that Skyrim will have it sometimes.
You may wonder what the definition of beautiful is. It's a tricky question. Highly subjective of course.
But according to me, I think these videos show some beautiful sunsets and sunrises:
http://www.youtube.com/watch?v=PIRwCOB-cw0
http://www.youtube.com/watch?v=3D6ukuohk2U
http://www.youtube.com/watch?v=PYmnXze3RN0
http://www.youtube.com/watch?v=KpuAnc8teE0
On a note, I think god rays (Crepuscular rays) is somewhat related to this topic. I think they should also exist. It makes sunrises and sunsets so much more beautiful (in my opinion).
Here's another thread of mine though, focusing specifically on god rays: http://www.gamesas.com/index.php?/topic/1154978-god-rays-crepuscular-rays/page__st__40__p__16908528__hl__god+rays__fromsearch__1#entry16908528