MMO’s are all about progression, permanence, and in my opinion a lot of decision making. All roads lead back to your character. What used to be a hot topic, but lately has been mostly ignored or looked over, is the idea of respeccing your character or undoing decisions you made to customize it a long the way. There was a time when any decision you made was absolutely permanent without any chance whatsoever of a redo. It was crazy stressful but at the same time it made every decision an important one.
On the complete opposite side of the spectrum is today’s willy-nilly spend your points wherever and redo them whenever mentality. There are no more important choices after you choose your class (and in some games even that is gone).
Respeccing should be extraordinarily difficult and something you rarely ever do. I’m not a fan of the 100% inability to undo a single mistake but players need to be held accountable. Back in the SI days of DAoC you would have to find a rare drop from a boss. There would usually be 20 or 30 people going and only a couple would drop. That’s one option that I liked. Another option is to go the SWG route where it’s not a leveling mechanic but a skill tree that you can spend experience into and consume a skill point. If you want that skill point back, you unlearn the skill but lose all the exp you spent on it–this is my favorite system since it is more liberal with the ability to undo while maintaining the drawback of absolute loss. Another option is to make you go on some epic quest and spend an inordinate amount of resources. Whatever the option, it has to sting.
Don’t think of the sense of quasi-permanence as a punishment, though. Think of it as an encouragement to use your brain and come to a decision about something important. Consider your character more than a whiteboard that can be erased at will and an opportunity to appreciate what you have even more because there was some weight behind the decisions you’ve made. Look at the bigger picture that comes into focus when the game plays less like an arcade game and more like a persistent world.
Update: The comments have turned this towards a discussion of the bigger picture: how MMO/RPG’s are designed. A piece of that bigger idea is the loss of connection between the player and the virtual world. Players are not living with the consequences of their decisions, social interactions are non-existent, and instead of fluid character development it’s this idea of constantly changing to be the best at any given moment in time. I recommend reading the comment left by filch as it is quite insightful.