To me, a powerleverer comes in several forms.
One is the type of player that cares nothing for the story, nor the development of their character. The 'goal' of the game to them is just to get to the top in everything they can.
The second is the type who tries to stay ahead of other players. Note I said players, not characters. The game to them is beating other players, not overcoming other characters. Their mindset is "I want to beat Bob from Kansas", not "I shall strive to best my rival, Sayita (Bob's character)". The game is a race.
Then there are the RP powerlevelers. These are sometimes 'forced' PLers. These people have a set vision of what they want their character to achieve, but go beyond that for OOC reasons. Much of the time it is out of pure boredom, having to level one ability to support an unrelated one, or wanting to see higher level features. After they get to the higher level, a lot of them will not RP that they are at that level, but hold to their original vision.
PowerQuesting falls under this last category more often than not, though it is a great part of the other two as well. I say that questing is ooc for the main reason that I do not know a single person who will go up to a relative stranger and ask if they need help, or ask them for a quest. It feels so unnatural to me, I simply can not do it.
One way to tell if a player is powerleveling or powerquesting is the way the talk to other players. If they use numbers and talk about maxing certain skills, or ask if you have done X quest yet, or keep a notched belt of how many quests they did complete, then you know they have been doing a bit of powerleveling/questing.
The last type of powerlever is the pre-created character. These pure RP folks start playing as a more powerful character right from the get-go, and occ PL in their RP off time to get to that level. They completely disregard that leveling, as their character was already -at- that level when they started. A lot of these folks never even get the leveling finished, and become known as the pretenders, or godmodders if they get too greedy in their 'trained' skills. Most good RPers will go along with these folks as long as they keep their supposed skill levels low enough.
A great deal of roleplayers are migrating to this last type, as they wish to play something other than the newb to hero stereotypical role. I have heard the phrase "I am not even going to level after the wipe" from a large number of people. This is disturbing, and is what is causing the huge rift between them and the other types of players. Something -is- askew, and it is hard to put a finger on.
By the way, I play a different version of the last. When I create my characters, I play that the stats I receive -are- at the max, and they can get no higher. No leveling is needed, and would actually be out of character. Some may think of that as lazy, but then, they have never played the type of character I do.

And Xillix is correct. If I was to play a higher level character, I -would- have the stats to back that up. Perhaps when the game becomes less geared towards PLing up to be a fighter/hero/ulberslayer, you will see some more advanced characters from the moon.
Second by the way: The only type of player I have a problem with is the godmodder, who is not a PLer at all most of the time. You could almost call them a powerplayer, as it is their aim to be better than other players, but without ever doing anything.
There is room for every other type of player (except grievers and leeters), and I have said before that they are ALL needed. Well… perhaps the maxxed out-good at everything characters could be fewer and further between, as they do demean the players who do set limits for themselves, and try to play just a certain role. That is something for the wish list, though.