There is a new recent feature in Plasma that I think deserves a little explaination about the choices made. Right after the "Tokamak" Plasma meeting, the Plasma panel had a little "cashew" toolbox icon on its right that did nothing. Now clicking on it pops up a new widget that is intended to be a drop-in replacement for the panel configuration dialog accessible from the right mouse button click on an empty area of the panel (and somewhat to replace the entire right mouse button menu, that is neither not very accessible, intuitive, or discoverable).
Now, clicking on the toobox icon pops up a new widget (with alpha-blending goodness if you have compositing enabled). This entity (which is a drop-in replacement for the old configuration dialog) can do several things, like adding widgets, killing the panel, and resizing/repositioning the panel.
To resize the panel, it is sufficient to drag the window edge, like any other window, and by dragging the "window" itself you can move the panel to the other screen edges.
Now the interesting part: moving and resizing the panel is just like formatting a paragraph with a word processor. But why?
In KDE 4.1, the panels will be able to automatically grow/shrink when you add and remove applets (in the future, applets like the task manager will also be able to make the panel grow or shrink), so the user will want to be able to set where the panel starts, the direction where it grows and maximum and minimum sizes that limit the growth/shrinkage of the panel. In a way, it's like a paragraph aligned to the left, center or right of the page, which explains the three "paragraph" alignment buttons :).
At this point, to complete the metaphor what could be better than a ruler similar to the one used in word processors to decide the indentation and margin sizes? Other types of controls would have been possible, like simple handles at panel edges, but this is the only one that is able to really manage the concept of growing and shrinking panels in an intuitive manner. Since a video is worth more than 1024 words, here it is: