My first post — Mouse Tips — was quite popular, so here are three more!
Right-click on a blank area zooms to the selected area. This is MUCH FASTER than using the zoom button on the main tool bar.
Select an object, then Shift + Left Click and drag it to break all the pipe connections as you move it to a new location.
Select an object, then Control + Left Click and drag it to make a copy.
I demonstrate these in this 1m19s video.