Search functionality is crucial to any collection of scientific papers.
A simple search field would search through titles only.
An advanced search option would include the following fields: AUTHOR, TITLE, KEYWORDS and ABSTRACT.
(I do not think that searching full-text would be feasible, esp. that many original PDFs have a range of encoding-related problems and there would necessarily be plenty of misses.)
Search should also be available in "published" (shared) folders.