In Revit 2010 the shared coordinate system is now more visible to the user.  By default you can click the "Reveal Hidden Elements" button to see the coordinate points.  I want to go through some typical scenarios where shared coordinates would be utilized, along with a few quick videos to better illustrate the workflow.

Acquire Coordinates

Common scenario for "Acquire Coordinates" would be where a project file exists such as a CAD or Revit file containing the site information.  This linked site file is at the correct location, and will serve as the coordinate system basis.  The file would be linked into the main Revit project, and the "Acquire Coordinates" option would be used. 
 
Additional information is in the Revit 2010 Help file, under "Acquire Coordinates".  Video example below:

Video Example

Publish Coordinates

This scenario is used where the Revit project will serve as the coordinate basis.  This workflow actually modifies the linked file. For a Revit link, the host project's True North and shared origin are recorded in the linked project, based on the current location of the linked instance.  For a CAD link, the shared coordinate system will update the UCS in the CAD file.  You will be prompted to save these changes to the CAD file before closing out of the Revit project or after moving the link at any point.

Additional information is in the Revit 2010 Help file, under "Publish Coordinates".  Video example below:

Video Example

Project Base Point and Survey Point

The project base point defines the origin (0,0,0) of the project coordinate system.
The survey point represents a known point in the physical world, such as a geodetic survey marker.
When Shared Coordinates are being utilized, you will see the Survey Point change to reflect the shared coordinate system.  For example, acquiring coordinates from a linked CAD file will move the survey point to the origin of the CAD file by default.

Video Example

The Help files have additional information on these topics and more.  I would recommend starting on the "Shared Positioning" page and working through the various topics.