1. Search Bar: new icon required for the “search” action, design required to visually associate an “action button” with a textbox, design for showing search suggestions, design for making it clear that user can select the search engine.
2. Icon Polish: use shapes and metaphors from the existing *Stripe themes, but unify (and soften?) the colour palette and update the edges, detail, styling and gloss to match better on Vista, with modern XP apps, and OS X.
3. Tab Strip: improve distinction of selected tabs, differentiate appearance of background tabs from tab strip, optimize close tab button for use on all tabs.
4. Buttons in Textboxes: make buttons that appear in textboxes distinctive and provide affordances to indicate that they are “clickable” elements.
Personally I think there are definite usability enhancements in some of the changes. I don’t like that the style moves away from the default OS theme, though. This is one of the areas where Opera excels; the fact that it can use native UI widgets rather than having to mimic them.