I have been using the Notes 8.5 beta for a month or so now and one of the best features is the federated calendars.
Essentially this feature allows you to overlay additional calendars with your own. For example you might want to add some of your colleagues calendars or you might have an events calendar for your organisation. Well with Notes 8.5 you can simply select which calendars you want to overlay with your calendar. On the left hand panel of your calendar go to Show Calendars and you can choose to Add a Calendar...
You choose a calendar to add and you have the option of using a user's calendar, Notes Teamroom Calendar, and even a Notes application Calendar. The ability to bring together disparate calendars is awesome. We have been able to look at shared calendars in the past and use Group Calendars to kind of compare different calendars but this is just seamless calendar overlays.
An example of how I am using this new feature is leveraging TripIT. TripIT is a new Web 2.0 type service that enables me to forward all my airline and accommodation bookings to it. When I email a booking to it the clever team at TripIT somehow automagically reads the itinerary and adds it to my TripIT Calendar. Now I can access my TripIT calendar directly via a web browser or via my Blackberry Bold's browser but I can also subscribe to an iCal feed.
So all I do is Add a Calendar, select an iCalendar Feed as the source, enter the URL to my TripIT feed, select a colour, and their you go. Your flights etc are automatically added to your calendar!!
So all I do now is email all my flights to TripIT, there secret sauce reads the document, and they add it to my calendar!! Now there is a reason to upgrade to Notes 8.5 when it arrives!