I tried two applications for uploaded photos to flickr in Linux. The first is juploadr-1.0, which crashed many times for me and after an entire day of trying I just couldn't get all of the 500 photos I wanted to upload, uploaded. I had much better luck with kflickr-0.6. There seems to be a trend of quality KDE applications (amarok, KDE itself, k3b). Not so many Java or Gnome ones, but I digress. Originally I liked the way of editing descriptions and tags in kflickr but then I realized that neither of these applications compared to flickr's organizer feature, so it didn't matter. kflickr did crash on me if I right-clicked anywhere on the imported images.
kflickr would pop up a dialog box if there was a network timeout and stop uploading entirely whereas juploadr would skip that file and then try the next file. Why it doesn't just retry that file again, I'm not sure. This "feature" turns out to be more of a bug because after it has skipped about 1 out of every 20th photo in my 500 photos, it ended up crashing at some point. So I had a big swath of photos that had not yet been uploaded, but I also had some other photos that had not uploaded because they were skipped. Finding out which photos were skipped would be impossible.
kflickr basically worked on the first try. I got the timeout dialog a few times and thus had to click "OK" and then hit the "Upload" button to resume but in the end it did finish up. For now my flickr uploading application of choice is flickr.
One that I really want to try but have not had luck with is flickrfs. It looks really neat, but I had problems mounting my flickr account on a local directory.
Updated (2006-08-12): Another advantage of kflickr over the competition (juploadr) is that it loads thumbnails lightning fast. With juploadr I was waiting forever for all of them to load whereas flickr took less than a minute for 500 photos.
Updated (2006-08-15): So the problem related to jUploadr timing out is apparently fixed, simply by adding -Xmx512m (for example), to increase the amount of memory available to the Java VM. This will be fixed in 1.1 which is in Beta right now. The other advantage kflickr has over jUploadr right now, however, is the ability to set the title or description for one picture and then to easily move to the next or previous picture, just like you can do in flickr's Organizer. On the other hand, this is a "feature" for jUploadr because it is dangerous to have too many features like this in the client. If the client crashes or your computer crashes you will lose all the captions (for example) that you created locally on your hard drive. This is why I prefer using flickr's organizer. For a small number of pictures, doing all the titles/descriptions in the client quickly can be handy... Another thing, kflickr remembers the tags you used previously (for autocompletion) which just prevents typos in your tags more than anything. Both clients provide a good batch editing mode.