I've used a variety of services similar to this over the years; delicious, spurl and currently diigo.

My use case works like this:

1) find an interesting website / article 2) highlight a paragraph 3) click the magic button (ie: diigo's chrome extension button) 4) save the url along with the high lighted text and a tag 5) my blog then pulls in this info from my diigo user's rss feed and displays it to visitors

I'll be checking out google's effort, but I can't see me moving away from diigo unless I have to.