From what I can tell D3DX is just a helper library for Direct3D IM -- its not a replacement. For the most part almost all your code will use Direct3D IM functions and interfaces. Basically D3DX is there to help with some of the more difficult parts of Direct3D IM like texturing and initializing. But you still be using Direct3D IM for the most part.

Of course I might be wrong, but from playing around with it a bit, this is what I have found.

--TheGoop

TheGoop has it right. All D3DX does for you is take some of the initialization burden off, add some nice texture loading featues, and provide some nice math routines to handle what used to be in the old D3D framework code. You still get to (have to) use DrawPrimitive, vertex buffers, render state changes, etc.

There is a memory leak in D3DX, though, so I advise you not to use it =(

with the new d3dx, you can develop in a similar way like ogl (transformations, standardobjects...). Is it still worth to use im? is there a real speedpenalty?

Where is this supposed memory leak located? And have you contacted the DirectX group at Microsoft and filed a bug report on it?

A _great_ thing about D3DX is you can use as much or as little as you want. You can just use the texture-loading functions, the 3D math library, the sprite library, the D3DX Context interface for easy intialization, and the Matrix Stack object, without touching any of the other components.