Thanks for the links.
The FAQ only contains 4 suggestions for icloud.com:
1) I've tried in both IE, Chrome and Safari. Same in all browsers.
2) Birthdays are fine, but dublicate.
3) No warnings shown.
4) I've several times switched between applications and logged in and out.
As for the general issues:
I am sure everything is set to sync on the iPad.
Another funny thing is it stopped working from January 1'st, 2013.
Guess I'll just have to switch all calendars to Google Calendar...
I had the same problem today. Just started out of the blue....Calendar Events would download from iCloud to the iPad, but any new Events or modifications to existing Events made on the iPad would not upload to iCloud.
Spent about 4-hours trying to get it working. VERY frustrating....
Randers4 helped me in this thread above.