Richard,
Rearranging the graphs positions on the page is a bit painful. You have to move your mouse between 2 graphs and you will see a dashed line that allows you to resize them.
Also, you cannot really "move" graphs around, you can only "switch" them by clicking on the two curved arrows at thw end of the dashed line.

Speaking of which, is there a plan to allow a more "drag an drop" functionnality, like when using ajax on a web site?

Yes, we are working a new drag-and-drop interface that will address this....for now, the trick is to work with display windows independently of the view types, although this example is a level of complexity beyond the usual...I have the file and will see how close one can come.

FYI - this has now been addressed in 2.6.