I think that someone isn't a newb when they dps prgreses so that there auto attack is no longer in there top 3 dps - for casters its when they don't oom in 3 seconds =)
I would say it is a lot easier to shed the "newb" label vs. the "noob" label. After playing for a couple of years now, I know how the game works. I know the roles of the different classes when running in groups or raids. I no longer need to ask questions at every turn, or for someone to help me with a quest. In that regard, i'm not a newb.However, I am still constantly learning new things about this game. There are some things I will never know, like what it was like to raid at level 60. I like to surf Wowhead at work when I'm bored, and I am always coming across random new items or spells that I didn't know about. While I think I know a lot about the game (and I do), I don't know everything. In that sense, nearly everyone is a noob at one point or another. The thing is to not be ignorant about it. Someone who THINKS they know something and are in fact wrong, is a noob. Someone who is eager to learn more but still knows the basics, is neither a newb nor a noob. They are just a player.
You will never stop being a newb. There's always something in the game you don't know.For example: just 2 weeks ago I discovered that I could join a BG and/or see my honor by pressing "H" (and I've been playing WoW since 2007).
Newb: Someone who doesn't know the game well due to inexperienceNoob: Someone who can't even grasp fundamental concepts of their character, gear, boss fights, etc even after explaining to them and trying to help them out.Example of a Newb: a level 10 paladin asking where to get a pet. It's his first character, maybe he missed the part about combat pets in the manual (I did!)Example of a Noob: a level 80 death knight in half tanking gear, half dps gear, who doesn't know his rotation or gemming even after members of the guild have tried time and time again to explain to him how to gem and gear a dps death knight.Treat newbs with respect and try to help them. We were all newbs once. Put noobs on ignore. We don't need to put up with them.