I do not know who Red John is, but I have a few things to say. 

1) The writers would be insulting the viewers' intelligence by revealing PJ as RJ. 

2) That Susan Darcy lady must have a skeleton in her closet!

3) At the end of the most recent episode, (5 x 03) did something not seem off to you when Lisbon goes to play poker with FBI and finds her boss, CBI director (Bertram) there too??! That scene has a weird vibe to it and I can see RJ having something to do with that gathering. Remember, RJ has a friend in the FBI. But I can't say for sure that Bertram is our guy because he seems taller than the guy in the mask in season 2 finale and because I don't see a director like that doing the dirty job by himself. 

i think its stilles in 03x03 when frye re-appears Patrick go to the house that stilles told him to go, he said "i know more than red john" so i think he has someone inside RJ force, but RJ doesn't realize that one of his close friends its a spy?, i dont think so, so the other posibility is that Stilles is RJ


sorry for my english im from Uruguay

I think Bret Stiles is Red John. He can manipulate people; in a Season 4 episode, he tried to convince Grace to join his cult; it seemed fairly easy for him to do though she declined but he was able to "hypnotize" her for a few seconds. He is very smart, he has the means to travel as he pleases, he has connections (as we can see all of the people that "work" for him) in and out of the police and the FBI. There's something really "weird" about him; he's almost likable though he can also be scary. He's not in a lot of episodes but his character reappears here and there with new elements every time. The fact that he's kept in the background shows that there's more to find out about him in future episodes or maybe the producers of the show are trying to confuse the viewers.