Allegedly, the 7990 will be in short supply when it hits the markets, presumably later this month. As you may know, the 7990 is essentially made from putting two 7970s together, although each are underpowered when compared to having two lone GPUs.
This is not to say that it is weak by any means. Not much is known about this GPU yet, except that it has been delayed by at least a month.
But this brings up something very interesting. For a while, AMD has been ahead of Nvidia for releases, and slightly behind in power. But Nvidia knew what they were going against, so they had the advantage.
Now AMD knows what Nvidia has released, but Nvidia didn’t want to wait to release the 690. This seems to be mostly for the market, not for R&D(Research and Development).
Instead, AMD made a less powerful 7970 clocked at 1 Ghz in the meantime.