One reason why I was really looking forward to KDE4 was the level of abstraction it offered from services and hardware while offering a lot of unification as far as end-user interaction and desktop integration.
One fantastic example of this has become PowerDevil, which was introduced around the KDE 4.1 time but is now standard in KDE 4.2. Its functionality is based upon Solid, KDE4's hardware abstraction layer (which also abstracts audio & bluetooth).
PowerDevil runs as a fully-fledged KDE4 service, meaning it doesn't need to be some awkward "TSR" or persistent applet in your system tray. That also means that it runs much leaner than kpowersave, which largely monitored events and then attempted to send system calls along to the appropriate background resources.
The PowerDevil coders may talk down the control panel UI, but it works rather well. And while it doesn't have a Plasmoid (applet) yet or much in the way of UI, the beauty of KDE4 means it doesn't immediately need to. Since PowerDevil is well integrated into the KDE4 desktop, KRunner displays all the immediate options you need when you type "power profile" into the runner dialog. Very nice.
This kind of desktop integration is exactly what will make KDE4 a success in the long run, and it's great to see projects like PowerDevil emerge that take advantage of what KDE4, Solid and Plasma have to offer.