I came know of this quite recently. I find it quite useful. Apart from being able share your bookmarks across browsers, you can now share them with others too. del.icio.us offers quite cool features for sharing your favorite bookmarks. You can share your bookmarks, tag them (i.e. use keywords to categorize them), find other users with similar interests and browse through their bookmarks. I find it a very good source for finding resources - a selective search for the topics you are interested in.
And to add to that, you can even have browser buttons to quickly add any bookmarks you find to your online bookmarks.
Here is my delicious: