Basically, it's now very possible, and very easy, to flip windows between taking up one half of a screen - and later on, restore them back to what they were with just one mouse movement or keystroke, the same as 'aero snap' in windows 7.
If you're interested in turning this on, and you're a trunk user, take a look at the 'Keyboard & Mouse' section in systemsettings, go to 'Global Keyboard Shortcuts', and search for 'quick tiling' in kwin.
After you've set them up (for me, it's meta+left and meta+right), make a window active, and hit one of the hotkeys.
If you're also interested in checking out the mouse drag, take a look at 'Desktop' -> 'Screen Edges' in systemsettings. The option you're after is 'Tile windows by dragging them to the side of the screen'. ;)
Next up for me? I'm not sure. I'll be sure to let you know when I do.
[oh, and sorry to planet readers for spamming you: i didn't realise planet would import my other kde posts when i added myself, and i promise i won't post again unless i've got something new to say now. ;)]