WordPress.org

Does this plugin convert all words in the title?

No. There is a user-configurable list of stop words, pre-populated with a host of common words, which can be used to fine-tune the resulting tags. Words like "and" or "myself" are excluded by default, but there might be other words which are germane to your blog which don't make for good tags. You might, for example, want to add the name of your blog to the list, to avoid an over loaded tag with no real meaning.

Will this plugin overwrite my existing tags?

No. The plugin checks for the existence of tags, and if there are none, writes them based on the title.

When are the tags added? At publish or save?

Tags are added to the post the first time it is saved, but not when the post is autosaved. In many cases, the first save may well be publish. In this case, the tags are added at that time.

Is there a way to reset the list of stop words back to the original?

Yes. In the Options page for the plugin, there is a check box for "Reset all ignore words to defaults." Clicking that checkbox and hitting "submit" will restore the original list of ignored words. BE CAREFUL! There is no way to undo this process.

Will this plugin put tags on my old posts?

This plugin will put tags on any post that is opened in the Write screen and then saved, assuming there aren't already tags on the post. However, there is no system in place to do this as a batch file, since in some instances, this would probably be more strain on the server than it's really worth. If you really need to get this done, I'm sure there's a way to create another script that opens and saves each un-tagged post, but that's not something I'm looking into.