Simon Baker at a recent WB press conference:

“The experience that we had last year, in the last season—it was really interesting because you have the arc of what a story is and what the story should be. Then you have the idea of the business outside of that, of whether it will continue or whether the story is finished.

“If you ask me, the original story that we started off with and laid out in the pilot episode many years ago—that story finished probably around the end of the second season. When was Bradley Whitford (in the show as a man who convinced Patrick he was Red John but was not)? Like third season? I don’t know. They all blend into one."

He goes on to talk about Jisbon so I won't include it here.  Just found his "opinion" (whilst among WB execs) to be interesting and similar to some thoughts expressed here recently.

http://entertainment.inquirer.net/155649/simon-baker-coy-about-rumored-end-of-mentalist

(Sorry about the wierd source material....Philippine Inquirer?)