Mercurius
Legend
Reported.
Huh?
As for the topic at hand, I like what Dave the Mage says -- no level limits, but you have to switch classes or "skill sets" -- at least in principle. I would add that power advancement would have to slow waaay down, especially after Paragon, otherwise you'd have absurdly powerful 500-year old elves, liches, etc.
I kind of wish D&D had a more "realistic" curve, so that the power difference in levels decreases the higher you go; of course you could also just slow down advancement to reflect the same developmental trajectory. Even though I like limitless possible advancement, there should be some kind of cap for specific capacities. If you look at skills in the real world, say hitting a baseball, there is a cap on how good an individual hitter can become. Albert Pujols may get incrementally better, or he could just maintain a level of mastery. It could be both: As he ages and his physical skills start eroding, increased mental acuity could keep his overall ability at a similar level, for a time at least. Every player has a different trajectory.
Ultimately it really depends upon the proclivities of the gamers in question, particularly: How important is "leveling up"? How frequently do you like to level up? What degree of power is preferred? Is there a "sweetspot" or a range? Etc.
They key for anyone, I would think, is finding a pace and level scale that is not too slow or little that it bores the players, but isn't too fast that they become jaded. This also relates to the total campaign length and the frequency of sessions. I believe 4E's recommendation of one level every three or four sessions is based upon the assumption that a group plays once per week; if it plays twice a month, advancement might be better every other session (so once a month); if only once a month, maybe a level each session. But again, it depends upon the group.