It doesn't seem to be possible to merge two galleries. For instance, I had a gallery called "WorldCon 2005", and I tagged everything in there as "WorldCon 2005", which created a new gallery called "Tag: WorldCon 2005". I can then merge them, but doing so actually _removes_ the tags from the photos and puts them into the gallery they were already in! What I'd actually like it to do is tag everything in that gallery and make the gallery a tagged one rather than an 'event' one.
In addition, it'd be great if I could create galleries based on tag intersections. I'd like to be able to tag (for instance) with "Edinburgh" and "Castle" and be able to have a gallery called "Edinburgh Castle" that consisted of all pictures in Edinburgh, of Castles. This seems like an extremely basic use of tags, and would stop me from having to do what I currently do, which is tag everything as being (for instance) "2005", "WorldCon" _and_ "WorldCon 2005" in order to get the filing right.