When mainstream DDR2 reaches 800MHz, we'll start to see a shift. Right now, even some mobos w/ the Socket T have DDR slots.
DDR2 sacrifices latency for speed, which is why 533MHz DDR2 is JUST good enough to keep up with 400MHz DDR (+33% speed). One of two things will happen to get it into our PCs:
1. Manufacturers start saturating the market, selling for cost or less, like with SDR and DDR.
2. Some games start using more than the current 3.2GB/s bandwidth in actual use, necessitating a change for the typical enthusiast.
3. DDR3 (based on GDDR3, maybe) comes out while DDR2 is still expensive, and turns out to be cheaper as well.