A couple of weeks ago I drew your attention to a trial we are currently running for F1000 Prime (see previous post) alongside this you can also set up an account and put their answer to Reference Management through its paces, F1000 Workspace.
The F1000 Workspace platform helps researchers discover and collect literature, manage references and prepare manuscripts etc. for submission. It consists of a web-based application, a browser extension, and a plugin for Microsoft Word. This means that you can use it to search for literature (F1000 products and PubMed), insert references into your Word document, but also collaborate with colleagues to embed notes captured through the highlighting tools directly into your work.
Plus you can add notes to PDFs!
For more information and guidance see the following pages http://f1000.com/librarians#tab/workspace