wget http://www.usebox.net/jjm/nautilus-flickr-uploader/deb/nautilus-flickr-uploader_0.03-1_all.deb
sudo dpkg -i nautilus-flickr-uploader_0.03-1_all.deb
sudo apt-get install -f
The first command will download the .deb package, the second one will install it and the last one will solve all the dependencies (it requires libxml-parser-lite-tree-perl and all of it's dependencies to work).
Finally, to get it working, restart nautilus:
nautilus -q
Then, right click one ore more pictures and select Open With > Upload pictures to Flickr.
If you don't use Ubuntu, visit Nautilus Flickr Uploader website for Fedora rpms as well as the source code.