This thread makes me laugh... mostly because I was going over Soren's estimates for level gains and my main character is only level 10 after 4 years of playing him. Granted, I hardly ever dungeon and so most of my XP comes from RP and the rare few DM events I've participated in, but it always amazed me how other characters can rocket past me in levels. So I'm kinda on the knife's edge with this one... in a way, I want to say "yes, make it slower to level" but on the other hand, I want to say no because I'm already levelling slowly enough as it is.
That being said, I do like the idea of players being able to self-impose XP caps to throttle their levelling... but at the same time, I don't see that being much use. As it is, players can easily cut down the speed they gain levels by avoiding repeatedly grinding dungeons or staying away from higher levels (though I will tell you, from my experience, the latter doesn't help you that much unless you're very low level). I think the players who want to level fast will always find a way to do so regardless of what is done to slow them down, while the players who want to take their time can still easily do that now. So I'm gonna have to say things are fine the way they are now.