I bought two Micron Millennia GS133 PCs on a Friday over the phone. I then called Micron for a price adjustment. A sales rep told me that since the PCs had not yet been built and shipped, I'd be entitled to and charged for the new, lower price anyway. He was billed for the higher price. When you buy your next PC, ask the vendor about its policy on after-sale price adjustments.
Most companies have a refund policy if prices drop.
Some vendors, such as Dell, have a price-adjustment program, but others, like Gateway, do not. And some rules are standard. For example, you're eligible for a refund only when the price cut applies to exactly the same model and configuration as the item you purchased. It's up to you to keep tabs on reduced prices and contact the manufacturer for a refund. Special promotions are excluded, and if the new, cheaper version of the system has a different component or extra features, you're stuck with the original, higher price.