In fact last we heard, James Vanderbilt (i.e. Zodiac screenwriter) was hired to write Webhead's 4th cinematic adventure. And that was just a week or so before the WGA Strike started last year.
Since then, it's been dead silence... until now.
Cinematical is reporting (via a trusted insider) that Vanderbilt turned his screenplay in just a few weeks back.
And according to their source:
"His story arc has encompassed two films, making Spider-Man 5 shootable at the same time. The studio saw dollar signs and is in the process of reworking his deal to snatch up the story arc."
It should be worth-noting that similar rumors surfaced regarding Spider-Man 3 a few years back. If my memory is correct, said rumor was 3 would feature Sandman as the villain, and then segway into 4 which would showcase Venom.
Those "shoot multiple superhero sequels at once" rumors also applied to X-Men 3 back when Bryan Singer was still supposed to direct.
Even if this is true, it then becomes a question of whether or not Sam Raimi and Tobey Maquire return.
Neither are contractually bound to the series anymore. Not to mention both appear to be busy on other projects.
Raimi's currently working on Drag Me to Hell for next year and a Jack Ryan reboot for Paramount aiming for summer 2010 release, while Maguire is attached to produce and possibly star in Robotech for Warner Brothers.
So for the moment, take this rumor with a grain of salt...