jUploadr, the Java-based Flickr upload tool for GNU/Linux, has just been updated to version 0.5. I tested a preliminary version of this for Steve, and it successfully uploaded ~200 images in one go. It now supports batch operations, default tags, streamlined error handling, and a lot more. Version 0.5 also includes OSX support.
This is exactly the tool I was looking for! Thanks Steve!
F-Spot allows one to tag pics and upload them to flickr, besides other things. I find it pretty useful, overall.