Depending on your build and your saddle fit, it can be really painful on long rides on the old keester....
Having less than usual padding on my bones, I have a gel seat (like on a bicycle) that fits on my saddle. Makes all the difference in the world, don't get a sore butt and its also fairly warm in the colder temps.
You can get them from Greenhawk (Ontario) for around $50 (if I remember correctly)