Eep...
Christopher Perkins: We know that players enjoy the experience of "leveling up," provided it's not onerous, and so we've built a system that allows them to level up more often. We didn't want players to have to "level up" their characters every session because that would get onerous; doing so every two or three sessions seemed more appropriate and palatable, and that's how the new system is currently built.
GameSpy: Has the road to the endgame been lengthened, level-wise, or is there a new upper limit to how powerful D&D characters will get? For example, will a level 30 character in 4th Edition be as strong as a level 20 in 3.5, or is a level 20 character in 4th Edition about as strong as an epic-level character in previous editions?
Christopher Perkins: The way character advancement works now, it takes fewer encounters to gain a level, but it takes roughly the same length of time to reach 30 levels in 4th Edition as it takes to reach 20 levels in 3rd Edition. The rate of level advancement is still being playtested, however, so the jury's still out on whether the final game will work this way.