I'm just in the process of upgrading my rigs from 1GB(WinXP 32) and 2GB(WinXP pro 64) to 4GB and 6GB. That would cost a tidy packet in DDR3 but a lot less in generic DDR2.
To those who think that DDR3 is the future, it might be, once the prices drop significantly. ATM it's no better and a lot more expensive.