What's new in Opera 10.0:
* Presto 2.2 Engine
* Performance boost
* 100/100 and pixel-perfect on the Acid3 test
* Auto-update
* Inline spelling checker
* Opera Mail improvements, including rich text composition and delete after X days
* Widget Improvements on Linux

Changes in Opera Unite 10.10 Build 1840 Dev:
With the new Opera Widgets for Desktop we managed to break the dependency between widgets and the browser interface. From now on you don't have to have the Opera Browser open to run a widget. Furthermore, each widget runs in a separate process and integrates with the platform much better. We also give into your hands a new widget mode called “Application” so you can equip your widgets with the system default window decoration theme.
These are just some of the many new features and enhancements introduced with the new Opera Widgets for Desktop.
For a complete list of features please refer to the article Opera Desktop Widgets Evolved.