I have to post this if for no other reason than this software has such a great name!
From their site:
Bookgoo allows you to upload, annotate, and collaborate with your offline documents in an online way. Putting your documents on our website is only part of the story. We allow your documents to be highlighted and annotated in the same way you would mark up a piece of paper with a highlighter and pen. Moreover, we allow you to then share your annotated documents with friends, colleagues, professors – really, anyone! In turn, the people you share your documents with can highlight and annotate your document as well and provide comments on your annotations. Bookgoo facilitates the conversation on the document.
Webworker daily (another great blog) has a good post about it.