depends on what you plan on doing with the computer, and how much money is a factor.
personally, I make need-based upgrades. I like to keep my computer near the edge of tech, but before making any major upgrades, I need to ask myself if there's anything to be gained from the upgrade, beyond cutting fractions of a second off of the time it takes to reboot or open up office.
edit: there's also the question of stability to consider. if you upgrade to something on the cutting edge, you might find yourself with a driver-less product that's constantly giving your trouble (*cough*64bitchips*cough*).