You switch tabs by keyboard?
No, using the sidescroll arrows at each end of the tab bar in Amule/amulegui.
If there's a keyboard way. it's not well documented.
I believe maybe 2% of the users would profit from such a delay, while 98% would be annoyed.
If you keep the delay small they won't even notice it - but they will notice they can sail across the categories faster using the sidescrollers.
As far as category usage goes there are 2 sorts - those who don't use 'em at all and therefore don't get affected, and those who do use them - most won'tl restrict themselves to < 5-6 categories for long. As soon as you go past more tabs than can display simultaneously a small delay is a win.
Perhaps delay when using the sidescrollers, but not when a tab is directly clicked on?
Speeding up display in general makes more sense imho. Maybe then the problem goes away.
Not over a WAN session (eg: remote X displays). Dumping a screenful of data just slows things down further. Ditto on a slow machine, etc.
(I do this kind of fairly regularly. Many of the places I'm at allow outbound SSH, but don't have outbound ports open to allow amule remote controls to get out.)