I have been having a lot of problems with KDE lately: the main panel freezes up quite often, leading to the whole system becoming unresponsive; the only way out is to power off and power on.
Looking for an alternative, I decided to try out Blackbox (I have sort of decided to stay away from Gnome for various reasons, BTW). Blackbox is very lightweight: you just get a window manager, nothing else. The advantage is that it is not resource-hungry, and the response (as well as startup) times are much faster.
To achieve the same levels of usability as KDE, you need to go for other components: iDesk for desktop icons and bbkeys for key bindings, for example.
I have set up iDesk, but it sure is a pain to have to create text files for each icon that I want on my desktop. But this is a one-off activity, so it's not that much of a PITA. bbkeys needs a newer version of libstdc++.so than I have currently, so I don't have an easy way to manipulate the windows via the keyboard yet.
One drawback with BB is that when you minimise a window, it seems to disappear into the ether; you have to delve deep into the menu structure to get it back. There is supposed to be a way to tear off this menu and make it more accessible, but I haven't yet figured it out.