Thank you for this very interesting and powerful plugin!
I'm just giving MediaTagger a spin, but I can't seem to find an IMHO key piece of functionality: how to apply tags to many images at once.
If the media library is rather large, the initial cfg would become a very tedious and repetitive process if going one by one. A place to select all pertinent images, which shall get the same set of tags would be very useful, I think.
Also may note that when using with the latest WP 3.12RC3, the switch to Media Explorer seems very slow (~1 min) for just 150 pcs in my local DB.