Just as a reminder/to inform the newbies, you can find a list of the mood faces here, or in the Links section towards the bottom of the [Dashboard] page (which I use as my main blog bookmark since it shows you the most recent posts and comments). You should be able to get to this page by clicking on Dashboard when you are in the wp-admin set of pages, but that still gives you a "you should not be here" error... Nathaniel can you fix that?
Anyway, to use the mood faces, scroll down below the post-writing window to [Custom Fields], select 'mood', and then enter whatever moodname you want to use from the list. This could be better, but that's how it works for now. (And note that you should not confuse this with the Mood option directly below the post-writing field; in this post I have selected 'cheerful' for that field.)