It's indeed going to be a massive overhaul - Symbian^3 devices will be getting an entirely new user interface, which should finally give the old girl a more modern face to compete with the likes of Android and iOS. Marc Driessen, product manger at Nokia Benelux, has confirmed that this update will ship around fall 2011, preceded by a smaller update earlier in the year.
The smaller update will replace the iconography, while the large fall update will make menus less deep (finally!). The fall update will also give Symbian^3 an Android-esque pull-down status bar, and the navigation bar at the bottom fo the screen will become easier to use. Widgets will also be freed from the grid pattern, and can be placed on multiple homescreens.
As said, the update will ship fall this year for all Symbian^3 devices - both existing models and future models.