Most blogs have a calendar for navigation but not for much else. I was thinking how nice it would be to enrich it automatically with other information like birthdays of people on blogroll, anniversaries, schedule of conferences I am planning to attend, etc.
Size of the calendar will have to get a little bigger, but mouse-over sensitive date specific details can be displayed in an area immediately below the calendar. FOAF and iCal/vCal formats can be useful here. Calendars are also amazing yet under-utilized advertising medium IMHO.