I think patrons annotating the catalogue could be very useful, helping people to assess an item without actually looking at the physical item.  Patrons could decide which printed resources they want to use without leaving their own homes.  But beware!  other people's opinions are not necessarily applicable to your own personal needs, thereby possibly denying you the chance to see something really interesting.  Also, some filtering process should be in place as you could imagine what some of the comments would be like.