One of the few limitations I run in to with PM has to do with quickly isolating selects of varying levels of value. Color class and ratings are very good of course, but you cannot view by these criteria in the pulldown view menu. I often want to quickly see where I am in my overall editing process by isolating current selects only (for which tags are perfect) but I want the ability to react with more than just "tagged" or "untagged". You should consider the addition of a few different types of tags to help in the editing process. In addition to the current "check", maybe an "x" or something, so that one can further edit while viewing tagged images only.
I know that I could change color class or ratings in these cases, but that does not allow for further sorting or selecting WITHIN a subset of selects...
