Shooting on Spider-Man 4 has been pushed back and the May 6, 2011 release date is in jeopardy, according to Deadline Hollywood.  The problem is the script, which has been on a second rewrite since the summer (see "Gary Ross to Rewrite Spidey 4") and is still not ready to shoot.  Crew members are being told to stand down until a new shooting start date is set. 

Marvel movies (both from Marvel and its licensees) have aggressively staked out the first weekend in May (Free Comic Book Day!) for years, especially for Spider-Man, so the date will not be given up lightly, but a script would have to be approved soon for production to be completed in time.