There appears to be a new, working private server out, and it has in-browser play, named CP-Pro. It looks like the owner is already working on custom rooms – which is great. This isn’t very popular yet, so be sure to snatch up a good username, and remember, don’t use a password that you have used before.
Looks like they are moving to a website, so their private server is now offline, I will update this post when they have moved websites.
It also appears they are using ClubPenguinV’s source, because at the bottom of the play page, they forgot to change “ClubPenguinV © 2011. All rights reserved.”.