I doubt it. The FDA works on its own and is not influenced by corporate actions. XNPT not releasing the news indicates to me its not positive. Last example that was exactly like this was orexigen (OREX). PDUFA date came and went, and next morning at 6am came the press release and stock went from 10 to 4 that day.
Actually, I was more saying that the FDA could well have faxed the news to Xenoport by now but the licensing agreement with GSK gives GSK control over how the public announcement (approved, CRL or delay) is made.
I came across an example of this with the Canadian biotech Bioniche who had ceded complete media disclosure to their partner, Endo Pharmaceuticals, of the outcome of a Phase III trial in bladder cancer.