How do I publish an ical calendar?
Make sure you have Calendar set for sharing in the System Preferences > Mail Contacts &amp; Calendars > iCloud
Confirm that System Preferences > iCloud similarly sets 'Calerndars' to share
Login to your iCloud www page (or at least set it up);
Select 'Calendar' from the WWW page;
Pick the one Calendar you want to share from the left hand side of the WWW page;
In the following dialog, click the [email] button and enter the email address with whom you want to share.  The email does not necessarily have to be coupled to an Apple Account/ID.


Optional steps:
7.  Check that you are able to get 'cc:'d on that outgoing email that 'invites' the other to join in sharing;
8.  Add a calendar entry;
9.  Ask your friend to check visibility of new entry on iPad
10.  Ditto for all other Apple devices.

When Apple's 'iCloud' makes the Calendar available for sharing, a Green Icon appears just to the right of the name of the Calendar.  This icon means the calendar has been made available.  It doesn't mean that anybody has actually looked at the calendar.

On your friends side, they should perform the following steps:


Open their email, and if necessary, check the Trash or Spam folders to find your invitation;
Accept;
Open their Calendar application, iCal;
Make sure that the 'visibility' of your calendar is toggled 'ON' with a check in the box appearing at the brown top margin on the left by clicking [Calendars];
It wouldn't hurt to have them try to add a calendar entry in a reciprocal manner to the same Calendar to see if you can see it.
If you are having trouble still, check that their Settings-> Mail, Contacts, Calendars -> iCloud is set to swap Calendars with the iCloud


If you have a falling out or otherwise part ways with your friend, you can easily 'unpublish' your calendar (or even just stop updating it) from within the iCloud website.

For extra credit, try to see if you can get the receiving device to 'ping' in response to new calendar entries.  This would be similar to push notifications.
Go to the receiving person's iPad Settings-> Notifications -> Calendar to get Badges and Alerts set to 'on'

In "Settings->Mail, Contacts, Calendars->Fetch New Data" you can setup what to do.  iCloud-> 'Push' seems to be fastest.

As per Q3, above, it seems that you still have to ask the person if they've accepted the invite and looked at a calendar entry.  MacBookPro plays well with iPad. I tested this out.  Not clear how well the published calendar works with PC users.