My thoughts agree with MythMage's (as such do with several of the previous posters).
I love Epic as much as I love the 'non-epic' levels. For those players and DMs who don't like playing beyond level 20, they don't have to. Adding Epic rules or a handbook doesn't forces them to use it. However, for those who like playing Epic (i.e. post 20 level play), adding a handbook and Pathfinder rule-play gives them, as consumers, something they very much want. Not providing such rules tends to alienate that consumer base.
I dislike the concept of 1st level Epic play or restarting into Epic after level 20. The transitions should be relatively seemless.
Some of the mechanical changes are necessary and so it doesn't have to truly be seemless though, but you should retain all of your previous class abilities (BAB, HD, spells, hp, etc).
I agree with an unspoken Cap. Forgotten Realms did so in that despite a large number of epic NPCs, you never saw nor heard of a 60th level caster of anything of the kind. Most were in the 20-30's range, with the most powerful or powerful reaching or barely exceeding level 40.
I agree with the concept of epic integrating or incorporating rules on achieving deity-status, battling lesser gods, demi-powers, Dukes of Hell, Demon Lords, etc. Likewise, nation-building can be covered at this level, (but it can likewise happen at previous levels as well, just often in different scope and magnitude).
Pathfinder Beta has largely taken care of most of the problematic absolutes (e.g. deathward) so you guys at Paizo are already ahead of the curve. For which we are grateful!
Crafting epic magic items (whether called artifacts of not) and casting epic magic (even if just 10+ level spells) is also a big part of it.
I concur that epic PrC's or classes should grant 'epic' class abilities, and not just bonus feats. Some feats is ok, but not without additional class features. The class features of many of the epic classes were great (void incarnate, legendary dreadnaught, etc).
As for Epic play only being able to happen in the Planes, I disagree.
In many ways, Golarion already hints at the presence (past or present) of epic NPCs. For instance, Geb and Nex both are recorded as casting spells beyond the ken of any 20th level wizard. Aroden was a mortal who became a god, and did all kinds of epic things.
You can have epic NPCs interact in reasonable ways that does not invalidate 20th, or even 1st level, players or NPCs. FR did it, and did it well. Golarion can do it as well -the superstructure is already there.
