It depends on whether you can wait some months. If the system you have now runs fine for the moment, then, well, waiting is always great.
Personally, I'd say DDR is worth the wait - I'll probably get a new system as soon as mobos hit the market. The nice thing is that the new AMD CPUs - as far as I understand it - will still be Socket A, so getting a DDR mobo is a fine thing, as both components, RAM and CPU are easy to upgrade.
On another thing, the NEW thing is the DDR RAM, and motherboards which work with it.
The other components like CPU and graphic card have nothing to do with it (actually, the AMD CPUs have been DDR for some while now, but that's an entirely different issue).