Version:            (using KDE 4.3.3)
Installed from:    SuSE RPMs

Please let me know if this should be sent to QT instead of KDE, thank you.

Let's say I would like to switch option A and B in the menu X. Or increase font and see how it works and if it does not, decrease it back.

Currently you would click on X, then move mouse, click on A, move mouse over X, click, move mouse over B. Click.

What I propose is <hold> keyboard shortcut (or/and modifier). For example let's focus on modifier, and let's say it is ctrl.

The same scenario would look like this:
* click on X, move mouse over A, press and hold ctrl, click, release ctrl, move mouse over B, click.

I.e. such modifier/shortcut would prevent menu from closing when triggering any action/option. The saving on movements are not huge if you count the single distance, but those tiny movements are saved on a daily basis, and accumulate.