It's easy to share calendars with friends and family right from your iPhone or online in facebook.
Remember that anybody you want to share calendars with does need to be using calendarised too. You can 'Tell Friends' from your iPhone by going to Calendar>Share (You can choose to tell them either via SMS or Email) or from calendarised in facebook (A Tell Friends popup will help you).
When your friend is using calendarised all you need to do is send them a 'Share Request'.
Your friend will be sent a message asking to share calendars - When they accept the request you will be sharing calendars. You can see theirs and they can see yours.
The sharing is managed easily with just 4 simple options.
(Remember to use the 'Refresh' button on the Calendar screen to make sure you are looking at the most recent activity)
Share settings are managed online in exactly the same way.