Difficult to say. I've been on Friday and Saturday, but I didn't see anyone from the top training. I will soon upload my photos, although there aren't too many, I was too busy watching and enjoying.
There were probably a lot of them who were training, though. Even this Tuesday, I still saw Jankovic, Serena, Azarenka, I heard that Rafa was on court 4, and I know that yesterday Tsonga was on court 12 and Ferrer could be seen on one of the small courts as well (yes, just on the day I wasn't there). The week before I saw Rafa, Fognini, Robredo, Wawrinka, Janowicz, Tipsarevic and Schiavone.