DDR processes data sets on alternating sequences, the sine wave analogy was really quite good - it really isn't any faster in actual memory latency, but "potentially" does a better job of keeping up with the processor in providing data. Alas, DDR only reaches its full potential in a hardware architecture that can take advantage of it.
I must say I am suprised Apple hasn't done anything with DDR yet.
On the same subject, slightly different flavor - we are in the process of transitioning all of our mac users to TiBooks. According to some sources, Apple requires CL2 however in the TiBooks we have received to date, it is all CL3 memory installed (the number refers to the latency).
Unless the processor understands DDR, it won't be able to use it. I don't think the G4 can operate with DDR, so if Apple stuck DDR with a G4, it would treat it as if it was SDRAM. So, unless Apple is able to convince IBM/Motorola to incorporate DDR into the next processor design, they are stuck with SDRAM. Hopefully they have. That's just my two cents.
Well, one wouldn't normally associate memory type with the processor... but DDR operates on the basis that the prcoessor knows it can send twice per clock tick. Otherwise, the DDR memory would behave like SDRAM, because the processor would send only once per clock tick, negatting the DDR's ability to do double the data transfer rate per clock tick.