The wait has been a long one, but Flickr superpowers have finally arrived for Photoshop in the form of FlickrShop. As you can see, most of the basics are all available, such as tagging, adding to existing photosets or creating new ones, setting privacy and even specifying dimensions so you don't have to do any of that heavy lifting with the Photoshop file itself. The plug-in seems to work pretty well, though you can only upload one image at a time due to Photoshop's single document UI.
Still, FlickrShop is a free plug-in from PixelNovel so it gets a thumbs up from me. Two versions are available - one for Photoshop CS2 and another for CS3.