Pixelmator, a Macintosh-only Photoshop "clone," has shipped. Before you get too excited, note that while it includes layers and some advanced Photoshop tools, it doesn't seem to have color management or raw file support. Moreover, some useful Photoshop tools, such as Shadows and Highlights are missing in this 1.0 version. Nevertheless, because it uses the OS-X CoreImage tools, Pixelmator is lean and fast. Perhaps it would be useful to a Lightroom user needing pixel editing tools who doesn't want to spring for Photoshop. A 30-day downloadable demos is available for Pixelmator, which retails for US$59.
I'm hesitant to mention the other Macintosh-only Photoshop "clone," as it's still in beta and I can easily crash it, but Chocoflop (hey, I don't name these things) is at version 0.66 and does have raw file support. The UI is a little less clean, but it does have some things that Pixelmator doesn't.