Ok, I'm going to add my two cents, because it's my job.
While I see what you are saying about the Rookie thread and I can see how some newbies need to learn, I feel this idea is pointless. We have two threads for members to RP in.
Borgin and Burkes is for anybody, meaning
anybody. This includes Rookie RPers, and/or new people to this site. This is where many members begin. Basically this
is the newbie thread, if you want to look at it that way.
However, there is another thread.
The Malfoy Manor is a place where more experienced members can open an RP and other experienced members can join. This is for members who like to post more than one liners. It is also a place where the RP has more depth and descriptive story. I am not saying that everybody who enters The Malfoy Manor is an experienced RPer, but who are we to say this member is experienced, while this one isn't? It's the members responsibility to judge for themself if they are experienced or not.
I also want to agree with what Lee said. Not everybody on this site can speak english well and/or it might not be their first language. This site is universal. So just because somebody doesn't put a comma here, or spells a word wrong there doesn't mean they are wrong. We see it as wrong because we know better. But the member who is from another country may think they are correct. Slowly, by RPing with respected RPers they begin to learn. Same with the one liners. I know quite a few people who didn't know how to RP at all and most of their posts contained one liners, (me being one of these people if you can believe it.

) But as they RPed with experienced people, their RPing skills grew. If we were to change that and put all the newbies together, how would they learn? They would just continue to post one liners, with their bad grammer/spelling. They would have no one to learn from.
So you can see now why I believe making a newbie thread would be just a awful idea. Thank you for the suggestion though.