wouldn't say it's a replacement for bookmarking stuff for yourself, more of a way of sharing things. You can see who else bookmarks the same sites/articles and follow their bookmarks, and it makes it easier to tag/find things you've bookmarked yourself.
there are plugins for firefox, etc. which make it work more like a normal bookmarks folder as well.
It's fairly tech/business heavy, but there is enough people on it to be able to come across interesting stuff every now and again.