I plan to add new memory to my desktop machine around the time I install Windows 7. A few months ago I checked the price on two more DIMMs of the same type that are already in the machine: $32 at the time. I should have bought then because they are now up to $50. Oh, well.
The cause for the upward shift? The general sentiment seems to be simple supply and demand. Some have it as demand for DDR2 has fallen, and others have it as the supply was too high.
I have decided not to wait and get it now.