New reports are coming in that Transformers 3 production will stay in the city of Chicago for three more weeks. This info first came from Colin Hinkle and Sam Nickelson over the weekend but it seems closer to confirmed as a new notice went up that production returned to Lake Shore East Park for the next two days at least. The letter to the right is thanks to Jeff at Pixel Rally, which shows that production will be performing more skydiving stunts from helicopters much like TF3's first week in Chicago around Lake Shore Drive with Millenium Park as the landing ground.
In addition, CBS 2 and Chicago Breaking News are reporting that 13 bus routes are being detoured "while crews continue filming for Transformers 3". The rerouting starts today at 7:00PM until Friday 6:00AM. The sites also report there "may be occasional closures at LaSalle Street between Jackson, Adams, Madison and Monroe." Thanks to Ray for the link.
Colin also said that Transformers 3 might have returned to Hotel 71 at Wacker Drive as they are doing something inside the hotel and also prepping in the alley way underneath it. He couldn't tell if what was being worked on involved cast members or TF vehicles as didn't spot either.
It seems a lot of pick-up shots are in the works with the re-visiting of various locations. So to sum up, Transformers 3 will be remaining in Chicago at least through the week with the possibility for another three weeks total. Current info though indicates a week is the more likely scenario.
Update: Jeff provided another picture, this one indicating the planned Lake Shore and Millenium Park shoot from the letter above has been cancelled with possible date change.