Nvidia decided to push the launch but the cards are available as we speak. G84 and G86 cards are ready and can start selling whenever Nvidia waves with its flag.
The launch is still scheduled for 17th of April but many AIBs (Add in board partners) conformed that they are piling up the cards for a while.
The volume production includes Geforce 8600 GT cards but they are still on hold due the bios issue, that is likely to be fixed before launch. It also looks that Nvidia will do the quiet launch.