I haven't had much experience from the player point-of-view, though I'd love to; I think I could do the higher levels of any class proud, bringing the pain down on the greatest foes, the darkest demons and the craziest gods. As a DM, though, I have taken numerous characters, of players past and present, through the upper reaches of power. Granted, I've also stymied many a party from reaching those vaulted heights, and sometimes, we, as a group, have had to labour to get there (such as going through four? parties to eventually see the 3rd edition eight-part official campaign to its conclusion).
As a DM, the high levels are a way to break through some of the humdrum that can occur when facing simple mortal enemies. It allows planar travel to become a little more common (and survivable), providing whole new realms to explore. It provides for greater setbacks in the party, greater wrongs to right. And it provides the opportunity to stand toe-to-toe with evil incarnate, or to dance with the gods.
As hinted at the end of Cordell's post, players have often found issues with higher-level play, some a little more obvious than others. He uses the term "broken". I can't say that I've ever found it broken, but there were points where room for improvement could have been made.
In 3rd edition, for instance, epic characters, whether fighter or wizard, had multiple attacks, and the effectiveness and purpose of them could be questioned. And as might be expected, epic level combats were of epic length; one combat would be an entire evening's event. But what can be done about that? You don't want to just scale up the hitpoints and the damage dealt at the same pace, do you? Won't players see through dealing 50 damage to a 400 hitpoint target as just the same as dealing 5 damage each hit to a 40 hitpoint target? I believe so, and I believe the 3rd edition designers did, too; thus hitpoints rose faster than damage, and SR and saving throws required some effort to keep pace as well, much to Griff's chagrin.
We never did get a chance to try the 4e epic levels, which is a shame. I'd have liked to see how 21st level and above worked out. Having played with the character creator quite a bit, back in our 4e days, I did make quite a few characters (or rather, notable NPCs) all the way to 30th level, and surveyed their advances and "snapshots" at various points. Unfortunately, I never did compare then to like opponents at those levels, to get a sense of how an encounter might ave played out. Anyone have any info about epic 4e?
I think regardless of the poll taken on the blogpost, epic levels are an obvious must. There's no reason to exclude them -- players who detest them can just start a new party when they tire of their advancement to godhood -- and there's every reason to include them, because who hasn't wanted to take on Orcus or Demogorgon at least once? Perhaps this next incarnation can get them right for those opposed, without alienating those like myself who had had little to complain about.