Opera 9.50 beta is available for download and testing. I'm a long-time user of Opera as my Web browser, e-mail client, and Atom/RSS feed reader. I've had some problems with earlier versions of Opera 9.x, which can crash a lot when run inside a VMware virtual machine running Linux, due to an memory issue related to VNC. I'm hopeful that 9.50 will fix this issue (and I've been testing it since the alpha releases for that reason).
That aside, the most interesting new feature in Opera 9.50 seems to be shared bookmarks. One of the things I like about Opera is that it applies fast text search to everything. So, if you are looking for a bookmark, there is no need to have them carefully categorised (although you can if you must). Instead, just start typing in some text from the name or description, or part of the URL, and Opera will refine the bookmark list with every key press. You very quickly get the short list that you need. It's great, but if you run Opera on different machines or in different environments (and I effectively run Opera in 6 different environments), you still have the issue of maintaining bookmarks in multiple places.
Of course, there are Web sites for storing your bookmarks, but it's much slower to bookmark links that way, and the search facilities that those sites provide typically aren't as quick and easy as Opera's search. With shared bookmarks, Opera synchronises your bookmarks directly from Opera to a service via the Opera Community site. Each copy of Opera that you configure to login to an Opera account will have its bookmarks synchronised there. For me, it is a genuine improvement over what I have had to do previously.