Nvidia's G86 based Geforce 8400 GS will make its debut on the 19th. The card was meant for OEM's only, but it looks that a few people will have them in retail from the launch date. The other partners will get these cards at later date, so there is no need for panic.
The magic of this low end affordable chip is that it supports both 64 and 128 bit memory interface while ATI's RV610 supports 64 bit only.
The first news indicate that the G86, a 120 square mm big core is going to end up faster than ATI's RV610, an 80 square mm 65 nanometer core.