I installed this latest version (november 2007) of directx. Got huge problems lol. I only play fsx so cant tell about other games, but in fsx got huge fps drops in some tough areas. Like from 14 fps I went to 9 fps. But that's not all. Even when I have 30 fps it's still not playable - there is a micro stutter each second. It also brought problems with sound - it's seems like it's over saturaded sometimes and makes things even worse.
Seems it's impossible to go back to the previous version.

I don't really care since I'm reinstalling everything in few days with a new motherboard, but just wondering if you guys had same experience with this directx version?

There's a Direct X 9.21??