Andreessen tried to build annotation in the original version of Netscape. His new attempt with something like Rapgenius... not sure about it. This dotdotdot thing seems like a reasonable way. Part Instapaper, part ebook reader, filtering the relevant texts upfront via a human social filter, seems better like annotating directly out of a browser.

No one is concerned to write something that will come back to you in a negative way? Not everybody who could sing should sing in public.

A negative way in what sense? Because you don't write good? ;) Or because someone disagrees with the thoughts and feelings you express?

In the former case, writing (more) often will help you improve your writing skills. The more often you do something, the better you get at it. However, you might want to keep these "exercises" private until your writing improves.

In the latter case, as long as you're being honest, thoughtful, and respectful (and not intentionally controversial or offensive) with the views you express in your writing, I'm not sure how it would come back to you in a truly (undeservedly) negative way. But, if you've lost your rose-colored glasses and are still concerned, write anonymously.