Many thanks to Ayako for finding and posting the link.
Keanu Reeves spent Monday, October 1, 2012 at one of the Hollywood studios. He arrived early in the day and was seen several times during the day taking a break for a smoke. Photos indicate it was dark when he left.
At this point it is not know if the studio work was for 47 Ronin or Man of Tai Chi. Regardless, the visit was most likely for post-production work.
Thumbnails can be viewed here. A video clip of Keanu leaving the studio parking lot has been posted on Youtube and can be viewed here.
Note: The paparazzi are rude in my opinion. Also from the clip, it looks like the parking lot that we saw in the Toluca Lake sighting.