My old Flickr iPhoto workflow used to be:
1. set tags and access control (public or private) using web interface
2. email photos from iPhoto
which was a error prone process to say the least.
Now, I do everything with the iPhoto by using the Flickr iPhoto upload plugin and the iPhoto Keyword assistant which automagically completes tags so you don't have to type them in labouriously by hand (thanks for suggesting it Boris!). If you have a Mac and are a Flickr user, check it out!
Another new version, asymptotically approaching 1.0.
Now supports arbitrary reordering of images via drag and drop Better supports unicode text everywhere (sorry about that!) New "Add tag to All" feature - adds one particular tag to all images, preserving others.
Issues, comments, let me know. Please send any crash reports by email.