Well, the new DDR3 still have high latency and not really matured yet. It's good that you got ur DDR2 at the moment. Furthermore it's way too expensive and not worth to get at the moment. Not good to be early adopters of new technologies
I don't see DDR3 becoming common or really affordable within the next 6 months, but adoption will be quite fast with Intel pushing hard. Besides, DRAM manufacturers are losing money in DDR2. They would love to shift to DDR3 if only for better profits.