I finally found the time to watch the latest video today. I liked it very much! One thing, regarding the prefab preview window: It is true that you cannot use the LMB to rotate the model, but just like in 3D view, you can use the arrow keys to move around. So you can strave to the side (and compensate with turning via the mouse) to rotate around the prefab. It is more cumbersome than the LMB-turning, but it allows you to view the prefab before putting it in.
Also, while watching the part with the wall lamps, I thougt it would be good to mention the "Offset cloned objects button" (the second from the right button at the top). If this is active, the clone will be set off by one grid unit (so it also depends on the grid size you chose) to the bottom and the left. So, if you want to clone your lights, it is best that this is not active as you will have to readjust the position towards the wall. It is useful, if you do not move your clones immedaitely or want to create several clones, but personally, I do not really like it and have it turned off all the time.