Well, I collaborate frequently with people on research projects.  This involves sharing research papers.  I do this through Mendeley.  However, they put a limit on the number of people allowed to be in one group and on the total size limit of the files.  I only have 5mb left on a group!  So, I am thinking that it would be nice to switch to something else.  The best thing I have found is: http://www.bioinformatics.org/librarian/.  They are open source and I can run their server on my laptop at home.  Also, they still have the annotation and highlight feature which is nice. However, it is all web based.  So, I am worried that some of my bigger pdfs will have trouble…  Also, I wonder how it will handle previous annotations and highlights.