Jo Rowling's latest newsletter mentions that she's doing a bit of work on book 7 at the moment. A scan of it can be seen here courtesy of Harry Latino.

"I am not writing as much as usual at the moment, because I've got a new baby daughter; however, I am doing a bit of work on Harry Seven when the mood takes me, or my sleep deprivation permits. In the meantime, I hope you find Harry Potter and the Half-Blood Prince worth a re-read!"


Source: Veritaserum