Has KDE 4 caught up with KDE 3 yet?

I'm not sure how one would go about maximizing a window under KWin via DBUS, but you can do it easily under a variety of EWMH-compliant window-managers (including KWin and FVWM) with wmctrl <http://tripie.sweb.cz/utils/wmctrl/>:

wmctrl -i -r 0x04000016 -b add,maximized_vert,maximized_horz

In addition to the window ID (-i), as shown above, you can also select the target window by WM_CLASS (-x) or title (default). You can also control other flags, such as 'sticky', 'above', 'shaded' and 'hidden', move and resize windows, switch virtual desktops, and change the focus.