Konqi
--the up, back and forward buttons have multiple functions, so if you press them a little longer (I and many others do) instead of the action you wanted you get a menu with posible places to go. I find that very disturbing for file navigation. There are also the half buttons, I don't like them either. You have to be very careful to press the zone you wan't. The UP button doesn't even need something like that, in my opinion. So the best looking solution for those buttons, until now, is like in firefox with noia theme.
Menus
--a general sugestion wold be to avoid the situation where after a 2-3 level menu you have many toggle buttons. example: konqi->view->preview, there you have a lot of toggle buttons. These cases should be avoided, or a smart aproach should be taken. One solutin would be to have these toggle menus appear in a persistent (is that the word?) window that has its own close button and is closed when we end playing with those options.
--also the intricated menus (kmenu can get complicated) should either be avoided, or a smart solution should be found. They could transform in windows in a clever way when things get complicated. This is not a kde fault but mostly of big programs like OOO, Gimp, Corel Draw.
--complicated menus. Some context menus (not many, but they exist) have a bit too many levels. One example is right click one image ->actions->set as desktop background->centered or tiled (I think it is translated like that in English). The third level is not necesarry. If you want it in some fancy way you just go to the desktop.
The fancy mouse over effect
should not exist for the taskbar, I don't like it for other things either, but I simply hate it for the taskbar, and it took me, a kde addict, almost 5 minutes to find the setting. It was default with debian testing.