There are several things that need to change before DDR3 becomes interesting at all.
■Price.
It's expensive beyond reason right now.
■Specifications
Right now most DDR3 doesn't stick to the specifications and needs more voltage than the standard 1.5 volt. Theres almost no difference between DDR3 at 1.8 and DDR2 at 1.8 regarding the power consumption. Add the higher frequency that might add more heat. So until the production matures a little, this is a turnoff for all those laptops sold. In addition the "sweet spot" (defined by manufacturing limitations like heat, maximum amount of chips per stick as well as the different computers memory controllers and memory slots) memory sizes aren't really available yet. If i recall it they were like 512 MB for DDR, 1024 MB for DDR2 and will be 2 GB for DDR3.
■Tripple Channel
There are or were rumors about intel considering triple channel for their next new CPU architecture. If the performance boost is similar to the one seen switching from single to dual channel, then people might be willing to pay a little more for DDR 3 than they are paying for DDR2.
I am willing to bet that intel will be the first to really switch to DDR3. Right now their chipsets support it but most mainboard manufacturers have seen the signs and offer DDR3 only mainboards in a very limited quantity due to very limited demand. There is almost no market for ECC DDR3 or DDR3 SO-Dimms which makes the DDR3 market even smaller. I suppose most memory manufacturers need to get their fabs adjusted to a smaller process to be able to produce within the DDR3 specifications at reasonable cost. Until that changes, DDR3 is just a waste of money.