iP2F is a plugin that makes it extremely easy to upload your pictures from iPhoto 2 Flickr.
iP2F also lets you create photosets and add images to existing sets and pools.
And of course your EXIF image meta data (camera model, exposure, etc.) is preserved.
All that and more in one clean, easy to use and modern-looking plugin, which lives right in iPhoto's File > Export...-menu.
But you don't have to take our word for it: Macworld gave iP2F 4 out of 5 mice.