The interface is only part of what's new in Opera 10.50, but it's a big part. Optimized for Windows 7, the browser has implemented design changes that feel fresh, even though they're not entirely original.
Windows 7's jump lists are finally supported by Opera. The implementation is similar to Chrome and Internet Explorer, and the sites you've added to Speed Dial can be accessed from here, as can frequently viewed sites. You can also initiate a Private Tab, which works like the Incognito, InPrivate, and Private Browsing features in other browsers to hide your browsing tracks.
Although you can bring it back if you like the old interface, the new Opera has hidden all of its menus behind a drop-down 'O' on the upper left. Along with bookmark and history access, you can reach your Opera Unite, Opera sync, and widgets from here. Those three features are also available from a small panel at the bottom of the browser.
Opera's location bar has finally gotten an overhaul that brings it to parity with the other browsers that allow you to search the Web, as well as your history and bookmarks. Opera's version is notable for its layout that highlights where the predictive text is coming from.
The under-the-hood preferences section of Opera has been redone to make it even easier to tweak the browser. By typing opera:config into the location bar, you'll get a window that lets you tweak settings like in Firefox's about:config, but with better labels to keep settings organized.
Opera 10.50 has gained the private browsing feature that the major other browsers already have, but it's also tweaked the look and feel of some of Opera's unique ready-to-use features. Widgets, Opera sync, Opera Turbo, and Opera Unite are now all accessible from a sidebar that can be hidden, or a slick status bar control panel at the bottom of the browser.
Opera's Widgets feature has long acted as its version of plug-ins. If you're not familiar with the widgets, they're like Windows' desktop widgets, but tied to the browser and synchronizable with your My Opera account. Now, users can take their widgets out of the browser and leave them on the desktop.