"Combine both the "teenage stage" and "first chipset syndrome", where you get the functionality but not performance until the second generation: then you sit in an unideal situation. Amongst other things DDR3 does bring better general prefetch performance and lower power usage for mobile situations, but it's not yet going to give you a better computing experience.
Perhaps AMD's AM3 socket (when it arrives next year), as well as future multi-core CPUs from both camps, will offer a greater need for tons of memory bandwidth. However, the current situation means that sticking with DDR2 is the best option for the foreseeable future: there's far more competition providing better prices, better engineered BIOSes and chipsets currently available. Therefore, unless you have more money than sense, leave DDR3 alone for the time being - it needs to reach adulthood before it's going to start talking sense."