And now I learn from Daniel Seidel that he has started a website, mycommonplacebook.org, where people can create online commonplace books and share them with others. The site needs some design work, I think — while it’s visually simple, as is fitting, it suffers from undifferentiated elements, so that the reading eye can't clearly distinguish the content of immediate interest from the wrapper — and it needs a name. “My Commonplace Book,” for instance. But I love the idea.
If you choose to make your commonplace book public, and then identify quotations by author, a reader can find all the quotations people have posted by any given writer. That’s cool. There are “Categories” too, which I think most of us would call tags, but because people tag so idiosyncratically, that’s not as useful a way of slicing and dicing the data. (Delicious suffers from the same problem, though there is so much data on Delicious that the tags are useful. As mycommonplacebook.org gets more users, it will become immensely more fun and profitable to browse. Check it out.