Adobe has announced that next major upgrade of Lightroom as well as next major upgrade of Photoshop will no longer support Power PC platforms on Macintosh. Only Intel based PC will be supported (both Windows and Mac Os).
This choice is to focus development on more new platforms (like native 64 bits) more than keeping "legacy" support, like Power PC, whose latest PC models date back 4 years ago, a time that in the IT world seems to be quite long.