Among the features to find with Midori 0.5 is the introduction of a Cookie Security Manager (accepting/rejecting cookes on a per-site basis in real-time), improvements to the kiosk/execute use-case, speed dial improvements, and completely configurable mouse gestures.
Some behind the scenes work is adding support for WebKit2 and improved extension loading. In terms of WebKit2 usage, there's still more work ahead for future releases of this lightweight GTK2/GTK3 web-browser. WebKit2 is the updated interface for the Webkit rendering engine designed to fully support a split process model where the web content is separate from the browser UI model.
More details on Midori 0.5.0 can be learned from this blog post.