The former Information and Plasma Widgets have been placed in the same configuration window -- now relabeled Display -- so you can see at a glance all the notices that you can receive. Just as usefully, the arrow to display hidden tray icons now expands on to the desktop, rather than expanding into the rest of the panel, where space is limited.
Even more importantly, notifications from other applications can now be configured separately from the rest of the system tray. Currently, the separate notification options are limited, but you can now choose whether messages from applications display, and whether the progress of routine processes like file transfers is shown. I consider this small improvement a major step toward helping users work without interruptions.
In System Settings, few new dialogs have been added. However, some dialogs have been promoted to top level items, making them more noticeable, and a few have been renamed to make their purpose clearer.
The reorganization is especially noticeable at the top level. Mercifully, the Advanced tab of earlier releases is gone -- it was essentially a dumping ground for configuration items that did not fit into the top level categories on the General tab. Moreover, the limited top levels of earlier releases -- Look and Feel, Personal, Network and Connectivity, and Computer Administration-- have now been reorganized into Application Appearance and Behavior, Workspace Appearance and Behavior, Network and Connectivity, Hardware, System Administration, and Lost and Found (Geek-speak for "miscellaneous").
For previous users of the KDE 4 series, this rearrangement may cause some confusion, since the organization of System Settings has changed before.
For example, if youre looking for Desktop Edges so that you can set the actions to perform when the mouse moves to the hot spots around the perimeter of the screen, you now have to go to Workspace Appearance and Behavior -> Window Behavior, instead of Look and Feel -> Desktop. However, the order in 4.5 is comprehensive enough that perhaps users can at last hope for some stability in the organization of System Settings.
One change that won't be in 4.5 is the complete management of Kontact and KMail by the Akonadi personal information management engine. Instead, according to the beta announcement, this change will be implemented in a minor release about a month after the rest of 4.5 is released.
Considering the recent problems with Akonadi managing address books and interacting with DBus and MySQL, this delay is probably for the best. Already, the second beta in Kubuntu upgrades Akonadi and address books without the problems found in the Kubuntu 10.4 release, but, given the complexity of the change, additional caution seems wise.
However, with that change, the redevelopment that has marked the KDE 4 series will be largely complete. Some refinement of the semantic and social desktops might feature in the next release or two, but what will happen after that is hard to say.
Will the next KDE releases focus on incremental improvements? Or is the development team already brainstorming for new directions? Either way, the KDE 4.5 release seems to mark the end of an era.