Big news! I've finally achieved one of my most-wanted misfeature fixes with KDE4: disabling the ugly huge-ass animated tooltips in the panel. I think a lot of others wanted this as well, so I'm hoping they'll link here.
The tooltips in question are the ones associated with the "plasma" panel that usually appears at the bottom of the screen. They are annoying because they're huge, they don't look like other tooltips which you might have learned to ignore, and instead of staying still or moving with the mouse pointer, they "chase" the mouse pointer at a much slower speed than it moves, so they draw the eye away from the focus of attention. KDE3's similar feature was much less annoying, and could be turned off. KDE4's apparently could not be turned off in general.
If you ask how to turn them off, you are usually told to right-click on the task manager and uncheck "Task Manager Settings"->"General"->"Show tooltips." That only disables the huge-ass tooltips in the Task Manager, which is one major source of the annoyance but not the only one. They still appear for all other widgets, such as the
Start "Application Launcher" Menu and the desktop switcher.
My new discovery: as of KDE 4.5.1, you can disable them for most other places by opening the configuration manager and selecting "Workspace Appearance and Behaviour"->"Workspace"->"Informational Tips." There is no option for turning them off, but you can set the amount of time before they pop up, and if that is set negative, they seem not to pop up at all.
Caveats: to really get rid of the tooltips you must disable them in both the places I mentioned, for Task Manager items and for the "Workspace" in general. Some people have expressed a wish to disable the animation of the tooltips without disabling them entirely; I'm not aware of a way to achieve that. I would kind of like to have the tooltip available in yaWP (only) - ideally with a click instead of a hover - and so far I've been unable to get that to happen. The only way it will display full current weather information at all seems to be in the form of the huge-ass tooltip I just finished disabling. I may have to switch to some other weather widget.
Big problem: the developers of the relevant software will probably consider the fact that this annoyance can be cured, to be a bug, and change the software to force tooltips on users again in some future version.
Remaining issue (one of many): I'd really like to disable the animation in the Task Manager when items are added or removed; I'd rather it just immediately cut to the new appearance instead of showing the other items growing or shrinking to fit, because again, the movement draws the eye inappropriately.