Just a short while after launching DirectX 9.0, Microsoft are preparing to release the revised edition, DirectX 9.1. This years Games Developers Conference, hosted in San Jose, California between the 4th and 8th of March, will be the most likely venue for the official announcement.
The new API will most probably offer some improvements in the various aspects of DX but will most definitely address some hardware and software issues which came up with the 9.0 version.
Although there is no likely danger of the brand new R-300's and NV30's becoming obsolete, a fight will most likely break out as to who will manage to come up with a product which will be eligible to carry the coveted DX 9.1 official hardware tag.
nVidia are currently in the process of tweaking their NV30 based cards for release so they may have some trick up their sleeves but it is more likely that the product is already set and will not go as far. There is however, a good chance that ATI's R-350, which will be retailed as the Radeon 9900 PRO, may be able to carry the DX 9.1 tag.
What that will mean in actual performance is probably insignificant, but it may be the deciding factor when someone has a choice to make between a high-end nVidia or ATI chip.
The real significance of DirectX 9.1 and 9.0 for that matter, will probably be felt sometime around the launch of the NV40 and R-400 based cards.