My Opera synchronization is a feature of Kestrel which is designed to let you keep the same bookmarks and speed dials on different computers with Opera installed.
It is designed to be as simple to use as possible, causing minimal disruption in your workflow. Therefore, you will not find a lot of bells and whistles in this feature. A status indicator is all you'll see after having logged in from the "Synchronize With My Opera..." menu item in the File menu.
What does it synchronize? Bookmarks, Speed dial entries, Personal bar items and your Web panels. The latter two are really just bookmarks with settings. You can pick which to sync in the login dialog, and the checkbox for Personal bar also controls whether web panels are synced.
Once logged in, Opera will remember the username and password, and log you in automatically the next time you start. If you don't want to be remembered, you must log out from the File menu before you quit Opera. (Who quits Opera anyway?)
How does it really work? The idea of synchronization is old, and many applications and electrical appliances have implemented ways to synchronize e-mail addresses, phone numbers or street addresses. Sometimes all, sometimes just a few of these. E-mail clients can synchronize mail and contacts against your phone, and some web browsers with the help of extensions can synchronize against online bookmark services such as del.icio.us.
Opera Synchronization relies on this community site, My Opera, to work. In our server rooms here in Oslo, there are a few database, application and authentication servers that receive data from Opera, process it, store it, and send it off to any other Opera installation that comes by with your username on it.
For Opera to send your stuff to the server, it goes through all your bookmarks and speed dials, puts them in a custom XML format, and sends it through a secure (https) connection to the server. The server will then store the items in its database. When another Opera with your login name comes by, Opera does the same as before, but the server will also look through what it already has to see whether something is different between the database and the new data. If there is something on the server which was not in the data Opera sent, it will return these items to Opera. Opera will then merge this with its own bookmarks.
When you add, modify, or delete a bookmark, Opera will store this status. Every so often Opera will connect to the server and repeat the synchronization process, this time sending only the changes to the server. Again, if the server has something new for Opera, Opera will get this back.
Opera identifies bookmarks by a Universally Unique Identifiers (UUID), not names or addresses. A UUID is a long number which is designed to be genuinely unique, thereby "Universally". Because of this, there is no way for two Operas to generate the same ID even if the address of the bookmark is the same. Although we hope to add detection of identical bookmarks in the future, it can currently happen that you get duplicate bookmarks if you have the same bookmarks at work and home before you synchronize with My Opera. To resolve this, you can simply delete the ones you don't need, and this will spread to the other Operas you have.
Source:→ Opera Team Blog