In yEd, the label placement consists of two part: a so called label 'model' that defines the set of valid locations of a label, and the actual 'position' which is its current location. These settings are available in the 'Placement' option of the 'Label' properties. With this approach, the user can restrict a set of possible locations and let one of the automatic placement tools do the actual placement.
For interactive editing, the SmartFree label model is often the most convenient one. With this model, a label can be moved at a constant distance to its edge by default. If the Shift key is pressed while moving, the label can be placed freely without restrictions.
Maybe this tip is interesting for you, too: http://yed.yworks.com/support/qa/562/