Dolphin file manager: Yes. Just a plain old file manager. It works well. If you shoot RAW with small .jpg in your camera, you can stick the card in your computer, open Dolphin in split view with one pane for the card, and another for the folder you want to use, hit "preview", and you can scroll through all of the images on your card and drag the ones you like into the folder. No need to import all of them in the first place. Another cool thing about just using dolphin is that you can configure it to open with a terminal pane in the bottom. The reason this is useful is that you can use the command line to move, delete, resize and modify images really quickly. I have a hard time convincing people of the usefulness of this. "I dont want to do terminal stuff" . But the command ' mogrify -v scale 30% sharpen 1 *.jpg' will scale every jpg in a folder and add a touch of sharpness after the resize. You can do this to 300 images in about 20 seconds. And that is just scratching the surface. Its worth learning.
RawTherapee: pretty nice, but resource heavy. Unless you have a 64bit system with at least 4g of ram, I dont recommend it.
DarkTable. Quite an amazing RAW editor, and the tethering option is similar to Capture One. It takes quite a while to figure out how to use it well however, and setting it up the way you want it takes a considerable amount of time. Also, if im not mistaken, the developer REFUSES to make an "export to GIMP" option. I think that he cringes at the thought of 32 bit floating point being reduced to 8 bit .tiff. I dont blame him, but still its kinda funny. Perhaps when GIMP 2.10 comes out with 32 bit support, he will reconsider. If so, I will most likely make this my primary RAW editor.
Photivo: Decent, but still a little buggy sometimes, and processing speeds are not super fast.
DigiCam: Good as an organizational tool but not a real good RAW editor.
UFRaw: Functional, but the color rendition is just weird. It feels alot more like a hack than an application. At least to me.
AfterShotPro: This used to be Bibble before Corel Corp bought it. This is the best RAW editor for lower resource systems I have found that runs on Linux. There is a decent plug-in set, and it is STABLE and very fast. This is what I am currently using for production. It is not opensource which bugs me, and you do have to buy a licence. But for what I am doing, it was worth the $50 investment.
GIMP. Not much more more to say. 16 and 32 bit support in 2.10, as well as a rumor about automated script creation. If this is the case, there is almost nothing you wont be able to do with it. One caveat, GIMP is GTK, so to make it look like the rest of your system on KDE you can use the QTCurve theme.
If you maintain your own website for your photography, Konqeror is the best tool on the planet for this. You can have your Wordpress dashboard in one tab, your home machine file system and your websites file system in split panes in another tab, and an ssh terminal in another tab.
Client Sharing and the "cloud".
There are a number of client proofing systems, paid websites with client login areas, etc, that all seem to work well if that is what you want, but if you create a shared folder for you and a client with dropbox, you have a real time proofing and delivery space between your computer and theirs. You can have one file for unedited, and one for edited. You can also make near real time edit changes while chatting with them. There is a really cool short cut with this as well if you are running Linux. If you shoot in small .jpg + RAW, and you import the images into a folder, rather than copying and pasting the small .jpgs one at a time into their proofing folder, you can open a terminal in the import folder and run "cp *.jpg ~/Dropbox/CLIENTS_NAME/proofs] and it will copy all of the small .jpgs from that folder to their proofing folder in a couple of seconds.
Get dropbox here: db.tt/rvzYR1B
I have my eye on OwnCloud for this in the future, but there are a couple of features that need to be implemented first. When they are, you can have your own 1TB sharable cloud folder system for next to nothing. Believe it or not, laptops or netbooks with broken screens that you can find on ebay for $50 make amazing home servers for this kind of thing. Dual core atom netbooks are my favorite. You can find them for $20, throw crunchbang linux at them with the "would you like to install a webserver?" post installation script, stick them on a shelf, and you have a 250gb owncloud.
Social Media Promotion:
Gwenview: has some great export abilities when you install the kipi plugins. Click images you like and you can export them in bulk to Flickr, Facebook, or even remote folders (i.e. a website folder)
flickrfs: a fuse file system package that lets you mount your flickr account like it was part of your file system. when you create a new folder in the "sets" folder, and drop images in there, it automatically populates to your flickr account. Development stopped on this in 2007, but it still works.
IFTTT: This isnt Linux specific (even though the IFTTT servers are Linux) If you have not taken a look at the website "if this, then that" you really should. It has all sorts of "recipes" that you can create to do different things. Like "if an image shows up on this website, post it to this account as well." Very useful tool. If you are creative about it, just think what you could do with a camera with wifi and IFTTT. One recipe worth considering is Dropbox to "any social media site". You can create a couple folders for different sites, and when you save to them, the images will auto-post.
So there is my possibly unnecessary ramble. The most functional Professional level photo workflow Ive found on Linux: Debian KDE, Geeqie, Dolphin, AfterShotPro, and GIMP. Client proofing with Dropbox.