One thing I find very useful in Lightroom is that if you select more than one image, any keywords not in all of them are marked with an asterisk. You can then delete the keyword if you don't want it in any of the images, or delete the asterisk if you want it in all the images. I find this a really helpful way of syncing keywords, or removing mistakes. I don't think there is any way of replicating this type of behaviour in Photo Mechanic, but if similar functionality were possible, this would be great.
Graham