As an avid photographer, I was somewhat dismayed that there is pretty much no commercial photo editing software for Linux.
Gimp is awesome, but doesn't support RAW files natively. Many RAW editors for Linux appear clunky and, to my mind, don't seem to render properly. Bibble (now, Corel's AfterShot Pro) is a worthy candidate but lacks without layering options.
Until yesterday I was starting to think I might need a new hobby, because if I couldn't find a half-way decent Linux alternative... Well, who wants to go with Microsoft again?
Last night I opened my Ubuntu Software Center (instead of Google), and I found this gem. Pixeluvo (http://www.pixeluvo.com/). The trial version is free (though you need an Ubuntu One account to download it), or just grab the .deb from scrolling down their homepage. From what I've seen of it so far, it's completely worth the US$34+VAT price tag, which represents excellent value for money!
Whilst proprietry software, the dev is keen for constructive feedback and suggestions.
Check out their website. If you're a keen photographer looking for a native Photoshop alternative/substitute, this could well be for you.
Oh, and it plays very well with my newly installed Cinnamon 2.0 on top of Ubuntu Gnome 13.10 install!