Update: Price cuts detailed below seem to apply mostly to "Upgrade" versions. Because Microsoft will not cut prices in the same degree worldwide they seem to have refrained from specifying the exact pricing even for the U.S. in their press release. What is clear however, is that they intend to make price cuts effective at the same time as SP1 is (officially) released.
Microsoft announced today price reductions across the board for retail copies of Windows Vista. This an uncommon practice for the software giant, who has decided to lower prices of most boxed Vista editions by 20% only a year after the OS was released. Vista Ultimate version will get a discount from $299 to $219, while Home Premium edition falls to $129, previously it was $159.
Despite of the fact retail boxed copies of Vista only represent ~10% of its total sales, Microsoft hopes this will incentive users to upgrade now rather than waiting until they get a new PC, in which case the machine would most likely come pre-installed with the software. As part of the announcement, Microsoft also said they will lower prices in 70 countries later this year along with the SP1 release, and that in emerging markets they will stop selling "upgrade" versions of the OS completely. No further clarification has been made regarding OEM copies and if these will also receive the cut, too, but it's somewhat safe to assume this will be the case eventually.
Though it may be completely unrelated, the news came only days after some controversial email exchange between Microsoft execs about Vista was made public, making for a bit of a scandal, especially in online circles.