Frankly, you're better off with just about any flavour of Linux on an Intel system than PPC Mac users are to begin with. At least you can get the major apps more-or-less running with Wine.
Kindle for Mac, B&N eReader/NookStudy, probably the Kobo Desktop stuff since the Borders app is reportedly based upon it: all Intel Mac 10.5 or above, or it doesn't work and there's not even the hope of one day getting it to.
So while it's nice that companies do Mac support, they're not exactly supporting nearly as many Macs as you might think, compared to what Linux users can do for themselves.
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