Tweakers Guide has put up a short review of DX9 b1.
Well, what is there to say.The benchmarks say it all actually: there's just a small gain in performance. Unfortunately there are problems and errors with some current software - even if not directly caused by DirectX 9 itself. Due to this, this beta is indeed not recommendable for "normal users", however, programmers will have some advantages of this as it is a SDK.
News source: Tweakers Guide
View: The Review