Faculty and students, I found a useful web-based annotating tool that you might enjoy as well. My colleague who is on Facebook referred this to me indirectly. It is basically a subscription based web site, but anyone can register to enjoy the first 30 pages of pdf, word documents or powerpoint prsentations. You can also create snap shots of web pages, then annotate. This looks like a wonderful tool to help you and your colleagues or friends collaborate.
Check it out!