I am so happy to have found this plugin! Hopefully my issue isn't PEBKAC.
I regenerated some thumbnails (both individually and in bulk) and everything went great. I've verified the new image sizes are in the media library and ftp. But my posts don't get updated afterwards. If I edit the post and re-add the image, then it uses the new dimensions. Obviously I don't want to have to go through that extra step...
Am I imagining an extra feature? I thought it was automatic. I have tested this on 2 sites on 2 different servers. One is an out-of-the-box theme and the other is custom - both use the WooThemes framework.
Thanks in advance for ideas and suggestions!