In explaining the move, Adobe cited Apple's announcement that the forthcoming release of Mac OS X Snow Leopard (10.6) will not support the PowerPC chip set.
From the press release: "With Apple's future development focused on Intel Macs, Adobe is aligning its resources accordingly. Customers are being notified to provide fair notice of any changes regarding the operating systems and hardware supported by Adobe solutions. By announcing these changes now, Adobe customers will have time to plan their migration strategy accordingly."
According to the FAQ document, Creative Suite 4 and Creative Suite 3 will continue to run on both PowerPC and Intel machines, but Adobe will limit all future updates to the programs to fixing "critical issues."
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