D/S doesn't matter, polarity matters. D must be positive, S negative. Whether it's placed "above" or "below" the load doesn't matter. 
I don't very much like that they don't discuss the DC polarity of this part. The only signs indicating it, are the few words in the description, and the symbol. There is no specification for the reverse diode drop, if one is present (which there should be, if the diagram is correct). Very easy to overlook, and easy to goof up in the design process!
Tim
I can respect polarity, but the fact that a MOSFET is inside make me think about S and D load position.
First thing is, if grounds are shared, so diode (-) is connected to MOSFET (-), in this case I should consider voltage drop on Vgs and place the load on Drain side?
Do you think there're construction particularities that MOSFET (-) should be source?
An additional question. In an Optoisolated circuit, ground of the load should or not be connected to controller ground? Maybe I'm doing wrong so GND shouldn't be shared becouse we're loosing physical isolation of the two circuits.
I'm always talking in DC-DC connections.