+1 just means "I support / agree with what I just quoted". Internet shorthand.
OneNote is part of the full version of office. Info here: http://office.microsoft.com/en-us/onenote/
Kind of along the same lines as Evernote
, a free program that does similar things. You can use it to collect and organize information, make outlines, that sort of thing.
I use it to compile policy documents and training materials, which I then export to Publisher (also part of Office) for formatting.
I don't use it for writing projects, though. I use the features in Scrivener for that.