In a recent chat with actor Dan Aykroyd, The Boston Globe got the actor to talk about the status of Ghostbusters 3:

I'm sure you get these questions a lot, so I apologize in advance...Ghostbusters 3? I've heard that the writers of The Office are currently penning a script? How is this coming along, and should we look forward to this movie seeing the light of day? RELATED: Vixen by Micheline Pitt Unveils Ghostbusters Retro-Inspired Collection

Dan Aykroyd: Script is commenced early summer. Hope to be in production by late fall 2009

We reported in September that Dan Aykroyd, Ivan Reitman and Harold Ramis are consulting at this point, and according to Dan, Bill Murray is willing to be involved on some level. The concept is that the old Ghostbusters would appear in the film in some mentor capacity.

Stay tuned for more details on the upcoming production of the sequel.