I'm still just using KDE 3.3.something; whatever's in Debian stable. I find that it remembers icon size settings independently for "icon" view (thumbnails) and "details" view (file listing). With icon view, I use huge icons; with details view I use medium icons.
I just go to the View menu option for changing the icon size to what I want, for either view option. Those are the only two view types I use.