What has modern technology revealed about the Mona Lisa?

The sound of her voice, that she had given birth and that there is a drop of modern orange paint on the 16th century masterpiece.

In 2004, scientists from Canada’s National Research Council used 3-D imaging to scan the famous painting which has darkened immensely since it was painted by Leonardo in 1507. Under layers of varnish which have obscured many details including her eyebrows, the Canadian scans found a lightly painted transparent bodice over her neckline of the type worn by new mothers in Renaissance Italy. Though the scanning cannot say exactly who she was, such information helps support the theory that Mona Lisa is the Florentine Lisa Gherardini who posed after giving birth to her second son. The scientists also found a small cap on the back of her head which is a good thing as loose hair was a sign of an immoral woman.(1)

In 2006, French engineer Pascal Cotte and his company Lumiere Technology used multispectral digitization to once again see under the years of grime and varnish on the world’s most famous painting. Their ‘true color’ Mona Lisa has a brilliant blue sky which must have cost Leonardo quite a bit as lapis lazuli pigment was extraordinarily expensive back in the day. The French company also found a single drop of twentieth century orange paint in the clouds above Mona Lisa but cannot confirm how it got there. (2) 
Lumiere Technology's scan
Lumiere Technology's find of orange paint
Theories include the possibility of a restorer dripping on it by accident while working on the canvas at the Louvre, but it could have been done in 1911 when Vincenzo Perugia, an Italian carpenter who worked in the museum, stole the painting and kept it rolled up under his bed. (He was caught two years later and no harm done. Maybe.)
Vincenzo Perugia. He worked at the Louvre but escaped being caught for the theft by not showing up for his police interview. Despite such behavior, previous arrests for thefts in Paris and inside knowledge of the museum, the Paris Police never suspected the Italian carpenter though they had his fingerprint on the frame of the Mona Lisa which the thief had left behind. Unfortunately, it was a left thumb print. On an earlier arrest, the Paris Police had only taken a print of Perugia's right thumb. 
The most intriguing (or hard to believe) finding comes from Dr Matsumi Suzuki, a Japanese forensic scientist who measured Mona Lisa’s features in 2006 to estimate the size of her skull and throat. He put her height at 5 feet 6 inches. These measurements then enabled his team, including an Italian, at the Japan Acoustic Lab to create vocal pitches and timber for how she would have sounded when she talked. They then posted their audio result of Mona Lisa's "voice" on the internet.(3)
Dr. Matsumi Suzuki
In 2002 Dr. Suzuki won Harvard University’s satirical Ig Noble Prize (for improbable science that makes one think but probably should not be continued) in honor of his work on Bow-Lingual, an interpretation machine to understand dogs. Bowlingual's dog translation service is now available as an app for cell phones. 

(1) NRC Scientists Discover Mona Lisa Secrets”. October 25, 2007. CanWest MediaWorks Publications Inc. Canada.com. 20/08/09. http://www.canada.com/topics/technology/science/story.html?id=dd098037-dce6-4a6d-90de-88ccc05c9e57&k=96188
(2) “True Colors of the Mona Lisa Revealed”. October 19, 2006. Lumiere Technology. 20/08/09. http://www.lumiere-technology.com/Pages/News/news3.htm
(3) Freire, Carl. "In Japan, Scientists Recreate Mona Lisa's Voice". 2006. Art Info. Associated Press. 20/08/09.