Dolphin still can't maximize to fullscreen or, at least, I haven't found the way to do it. With fullscreen I mean to hide the kde startmenu's toolbar. It'd great to can do it if it was possible.
With KWin you can make a window fullscreen via Window Operations Menu -> More Actions -> Fullscreen or by assigning it a global shortcut. You can access that menu by using the default Alt + F3 shortcut, right-clicking the title bar or right-clicking the application in the taskbar. If you want even more available space you can also hide the Places panel and the menubar in Dolphin. Dolphin has no fullscreen mode shortcut or button anywhere as far as I can tell unlike most other KDE applications. IMO it should, at least for consistency.
*** Bug 420851 has been marked as a duplicate of this bug. ***