I just pushed a pretty big update to org-caldav. Get it at

https://github.com/dengste/org-caldav

The short story: org-caldav now does proper two-way syncing. It's pretty
much a rewrite, actually. If you're already using org-caldav, you will
have to start from scratch after updating.

Please read the README before using this version. Most notably,
org-caldav will set org-icalendar-store-UID when doing the iCalendar
export, so every entry with an activate timestamp will get an ID
property like this:

  :PROPERTIES:
  :ID:       6cdf8805-8d1a-46ac-94fc-d225cac5f098
  :END:

If you don't want this, do not use this package.

Please report bugs here or in the github tracker. And please have
backups.

-David