I've run games at basically all levels. That isn't to say that there was a straight progression from 1st to epic; I've certainly never done that or anything close to that. I did run a campaign and then later tell the players to restat their characters as epic (in-game years later) and ran a few sessions with the characters in the mid-30's. I have not run epic or even 16-20th level in several years.
I do frequently start games at varied levels higher than 1st, and frequently do short-run games in addition to long campaigns.
As I primarily DM, my playing experience is more limited, and I don't recall ever having played above 12th level or so. I am planning to play in a short run game at 20th level, but that hasn't happened so I didn't add it to the poll.
Overall, my philosophy is that it's good to use the whole breadth of the rules, but for a variety of reasons most play should be in low to mid levels.