Still trying to make the transition from Lightroom to darktable. Tho for critical clients work I still use Lightroom on Win7 side.
As still learning darktable. And took a look at rawtherapee http://rawtherapee.com/blog/features
but not to my liking as unintuitive to getting things done.
darktable is more lightroom like with tagging and organizing as well as an extensive array of editing tools.Darktable 1.1.2
, on Flickrhttp://www.darktable.org/
Usually have images imported and tagged and organized on windows side first than boot up to Mint side when I have time to give study to learning as I go with darktable. Knowing my fallback Windows7-Lightroom is there if I need it.
Not an issue for a lot of my images but critical for clients like Getty and other's where fiddling around and learning is not optimal for delivering results in a timely manner.
After a long hiatus Lightzone may be coming back and then there is Bibble which is a paid version tho powerful program.
And Corel Aftershot Pro to look at. As well as Dikicam,Gwenview,etc..http://server.ericsbinaryworld.com/blog/2012/02/16/using-digikam-from-the-point-of-view-of-lightroom-user/
As DigiKam just out with version 3.http://www.rileybrandt.com/2012/07/31/linux-photo-1/http://scribblesandsnaps.com/linux-tools-for-serious-photographers/
More searching on google for photography editing and many more choices depending on needs and use will determine your final solution. And most of these are in the Software Center and easy to search for and install.
Remember to always have more than one location to backup your files to. Way too many have the one and if that dies then left with none. Always take the time ahead to plan and implement organization thru common sense folder structure and copious amounts of tagging which will allow for searching and finding in a timely manner.
Also will take time to find the program that fits your needs. Also more time to get a handle on delivering results that satisfy.