As you can guess, once installed, you can easily upload images to Imageshack via the Unity's app launched by simply drag-n-drop. To install it, open your Terminal and issue the below command.
wget –directory-prefix=/tmp –default-page=imgupload http://ubuntuone.com/p/mEL/ && chmod +x /tmp/imgupload && sudo mv /tmp/imgupload /usr/bin
Then download the ".desktop" file which ads the icon for launcher from here. Once you've downloaded it, simply drag and drop the ".desktop" file into the launcher.
So, from now on, every time you want to upload an image to Imageshack, simply select the image and drag and drop it to the "icon" on the launcher in Unity (you need to have installed Ubuntu 11.04 for this). That's it.