MoodMill is a new site that lets you post your mood and share it with friends.
The site's functions are very similar to Twitter, but updates are directly associated with your mood. Indicate how you're currently feeling on a meter of sorts, which has about four options for how you're day is going. Type in some descriptive text, and attach a URL if you'd like. Now you can see how others feel, make friends, track their moods (RSS option available) and track your own. You'll get a graphical representation of your mood and how it changes on a daily basis, as well as a calendar marking your moods and your contact's moods, too. MoodMill will also tell you when your last good and bad days occurred.
The interesting part of MoodMill is the ability to attach a URL to a stated mood, which offers a quick, visual association with this sort of bookmarking aspect of the service. There are actually several ways in which this site could expand, by way of connecting other users and building out its bookmarking and search features. Another service incorporating mood meters of some sort is Mojikan.