Habits was released last week, but before that, I had something like it on a private area of my website for me to use. This is what my Habits looks like right now (edited for brevity and to remove personal data):
Generally, I use Habits to help with Sharpen the Saw type of tasks — things I want to make sure I do every once in a while, but not necessarily at a specific time. Also, unlike a recurring event in a calendar, I can record how well I do with them (if I do them late, early, or skip them).