A photo of what is believed to be two Radeon HD 7970 (Tahiti XT) graphics cards was published over at the Beyond3D forums. These 28nm parts are expected to be released next month.
The first visual observation is that these cards are hefty and approximately 10 inches long - or around the same length as HD 6970. They contain 12 memory chips (as demarkated on the picture - the 12th being at the edge of the PCI-e connector), which suggests a memory interface of 384-bit - a novelty for AMD/ATI GPUs. There seems to be a provision for 2x8-pin PCI-e power connectors on the PCB - or upto 375W power. However, both cards are powered by the SIG approved 6-pin + 8-pin configuration, powering upto 300W. The two cards are powered by a 850W power supply. This is no doubt a power hungry card, and all this power seems to be fed through a mammoth 20 phase VRM.