It is interesting to see that another GT280 card is on the way, as to what it is, is a complete mystery,
I wager that the predictions above of it being a slightly higher clocked card (aka Ultra) with perhaps higher quality RAM. Say 650Mhz 2.5Ghz RAM and 1450Mhz on the shaders something like that, maybe higher on the shaders and the core IF they could get the manufacturing process perfected and perhaps a cool heatpipe based cooler.
55nm is coming, but I would not think the GT280 will be 55nm until October/November. The 9800GTX+ will most likely be the "test run" on the 55nm process, once they have perfected that then they will start scaling down the GT280GTX to 55nm.
A real surprise and unexpected "rain on ATi's HD4870X2) parade would be 55nm, high clocks, high shaders and fast RAM WITH 256SP. That would give ATi a bloody nose, especially if the prices were slashed across the board, however I cannot see that happening..............yet
John