Briefly: pro.imdb.com has recently changed its "Pre Production" status to the "In Production" status for Toy Story 3. This means that Pixar is done with the script and other pre-production stuff, and has moved on the next step of your favorite toys' next animated feature!
Just as a reminder, here is the plot outline as given by IMDb Pro:
Woody, Buzz, and the rest of their toy-box friends are dumped in a day-care center after their owner, Andy, departs for college.It is set to come out June 18, 2010, and features the usual gang of actors doing voice overs: Tom Hanks, Tim Allen, Joan Cusack, Don Rickles, as well as the other voice actors from the first two Toy Story movies.
I'll let you know when they start "filming" (recording voices and animating).
Source: pro.imdb.com (subscription required)