I'm using this for the first time tonight. It's pretty cool. Here are a couple of observations:
"Additional tags to apply to all"
I thought this would apply the values in fields that you specify as flickr "tags". Eg, I input the following:
[Country] [Area] [Places]
expecting those field's values to be added as flickr tags, but unfortunately it literally tagged my files on flickr with those strings.
It would be really great if we were able to do what I was expecting.
Resize Images
This would be more useful if you could specify just the value of the shortest dimension. Eg, You want to limit the size of all of your pictures to 1024, so MC automatically makes landscape pics 1024px high, and portrait photos 1024px wide.
Re-Uploading
I'm not sure how much power MC has over this, but it would really useful if when we edit a playlist of images and re-upload it to the same set (and to groups) MC would give us an option to "overwrite previous files" like it does when you upload photos to a MC Pix01 image gallery.