I started a new campaign at 1st level a few weeks back with the intent of letting it advance all the way up to epic.
I figure it's the only way not to have to deal with all the pitfalls of high level play at once. Scrying, teleporting and ressurections make give a highlevel adventure a whole different feel. These have to be prepared for.
And it gives me the opportunity to introduce epic level monsters and characters without having them suddenly appear at level 20. My previous campaigns were all quite low-magic, with the king's court wizard being one of the few 20th level characters. But in epic levels, I need a whole lot of 20th level wizards around.
So now I've introduced stories from the battlefront about wizards casting meteor swarms and fingers of death.
Also I foreshaded a 5000 year old dragon, advanced with the rules in the Epic Level Handbook. This thing is a CR 85, and will make sure the players won't assume they're the top of the foodchain for a LONG time.