Right now E.N. Publishing is working on our next campaign saga, which we intend to go through epic level. I just hope people are still playing the game in 2 years when the last adventure comes out. (4e was announced mid-way through the 3.5 version of War of the Burning Sky, and it really killed our sales.)
We're planning far in advance so we can set up legitimate epic challenges for the PCs on the same plane. I'd like to be able to playtest some of the encounters with my local group to see how complicated epic is, and to avoid pitfalls. I did once run a 20th level one-shot, and I foolishly put a pair of mindflayers in a single encounter, which turned everything into a horrid stun-fest.
Right now I'm playing in an 11th level game, though, using MM3 and Essentials monsters, and it is legitimately fun. It's a beer-and-pretzels game, so pretty much all we do is combats to play with our toys; other people run roleplaying-heavy games in other systems. My main take-away with 4e combat, though, is that the game assumes too damned much of it. I'd be content with two or three combats per level, and certainly not 10.