So would we use the DirectX 11 option if our graphics card were equipped with the requisite support? The answer is: sure, as long as the card can handle it at the resolution we're using. When playing the game with a Radeon HD 5750, we probably wouldn't use the DirectX 11 code path unless we had a 1680x1050 or a lower-resolution monitor because we like 4x AA. Armed with a Radeon HD 5850, on the other hand, we'd use DirectX 11 enabled all the way to 2560x1600 with 4x AA, as long as we didn't experience a slowdown in performance (and our experience suggests we would not). But everyone will have their own taste as to what frame rate is comfortable.
Having said that, should you wait for a DirectX 11 card to play DiRT 2? Decidedly, no. The DirectX 9 code path is so slick and beautiful that it's almost impossible to notice the DirectX 11 enhancements while playing. I consider these enhancements a nice subtle bonus if the hardware is there to enjoy it, but the game is practically just as stunning when running in DirectX 9 mode.
Are we saying that DirectX 11 will be useless? Absolutely not. In fact, hardware tessellation and DirectCompute 11 offer potentially massive visual and computational upgrades over DirectX 10. The problem is that, as a racing game, DiRT 2 isn't an ideal title to show off what these features can do. Hardware tessellation is particularly suited to show off organic shapes, but the stars in DiRT 2 are the cars, not the people in the stands. Anyone who wants to see what DirectX 11 hardware tessellation can potentially offer games should look for screenshots of the upcoming Aliens Vs. Predator game by Rebellion--the use of hardware tessellation in the alien models is absolutely drool-worthy.
In the final analysis, DiRT 2 is a great game with fantastic visuals and a very entertaining approach to off-road racing. However, it turns out that folks looking for the definitive DirectX 11 killer app will have to wait a bit longer, as the visual enhancements it offers aren't particularly noticeable in this title. But the option to use this new API certainly doesn't detract from DiRT 2, which is a laudable game that offers an enjoyable, compelling, and unique experience in the racing genre.