In trying to restrict the desktop area covered by the menu, Kickoff makes navigating up and down the levels of the menu structure far easier than moving between sub-levels. This structure means more mouse-clicks, and a higher chance of getting disoriented. This disadvantage is serious enough that Kickoff is a step backward from the classical menu with cascading sub-menus that it was meant to replace. Lancelot seems a better choice, since it displays several menu levels at once -- or, if you're really concerned about the menu taking up desktop space, the minimalist KRunner.
Fortunately, KDE does make both Lancelot and the classical menu easily available if you want to replace Kickoff. But, all the same, KDE should have a stronger default.
For me, one of the most welcome innovations in recent KDE 4 releases is the ability to group applications in tabs in a single window. Although I took a while to integrate it into my work habits, I now find it an ideal way to group related applications together so I can find them more easily and reduce the clutter on the current desktop.
The only difficulty is that the task manager on the panel does not show group windows unless they are from the same program. It's as though grouped windows and the task manager have been developed with no sense of how they are supposed to interact.
Akonadi is the KDE sub-system for personal information management. It abstracts information such as address books and appointments from any specific application, and stores it in a database, where it can be efficiently accessed by any software that needs it.
The Akonadi Configuration application in KDE 4.5 offers tools to help users ensure that paths are properly set. However, server configuration remains a black art. You can run a test to be reassured of such things as "Akonadi control process registered at D-Bus" (if you happen to know what that means), but if one of the test items fails, you can only fall back on trial and error to figure out how to correct it -- neither your KDE installation nor the online the KDE KnowledgeBase gives you precise information about what you have to do.
To make matters worse, while you are scrambling to get the Akonadi server functional, basic productivity applications like KMail are unusable. Consequently, I consider this defect by far the most serious one in KDE.
If I were writing a few years ago, I know how some KDE developers would respond to this list. "Where are your patches?" they would say, and, when I confessed that I was hardly a coder, they would snicker and suggest that I therefore have no right to complain.
I have some sympathy for this response. Commenting on someone else's programming is far easier than actually programming, after all. But, these days, KDE, along with the rest of free software, is listening more sympathetically to users, so perhaps these comments won't be rejected out of hand.
Moreover, most of these suggestions would not require radical revisions. Most are minor tweaks at best, although the effect some would have on users' experience would be considerable.
Overall, KDE has improved steadily in the fourth series of releases, to the point where I now consider it to be leading desktop innovation in both free and proprietary software. But even a leader can benefit from a few improvements.