After 3 years I am still using ATI HD4870 which only supports DX10 as the most updated DX. I admit that I took advantage of price drop at the time DX11 had been announced and upcoming. Come to think of it, however, I still consider it to be unfair to me. It seems not many games really take full advantage of DX10. A few games which support DX10 doesn't appear to be that graphically enhanced than they are under DX9. DX11, on the other hand, has a much more promising prospect. Now that it has become industrial standard, Dx10 is rather like a luxury than a necessity for PC gaming.
There is a belief among IT geeks here: you should update only every alternative generation for Microsoft product. Say, Windows XP is a great OS, so you should not update it to Win Vista. You should upgrade directly to Windows 7 (And now it comes the Windows 8......)