AFAIK non-Indians should not be taking any INR out of India and Indian citizens or NRI/PIOs can take up to 25000 INR.

I hear that the going rate for 500 notes in Bombay yesterday was 300 rupees

Here in London, Indians are trying to offload their rupee cash stash by selling them to unwary British intending travellers. They are offering it for 20-40% off for GBP, and I saw at least one person getting scammed (unfortunately I was unable to tell that person he was buying very expensive paper - although it is possible that he actually knew what he was getting and has a way to redeem them for their full value)