I have been using del.icio.us for quite some time now. The web interface is easy and the concept of having a social network based on shared bookmarks is still compelling to me. Now Buzz Andersen (an Apple employee) has posted an early release of its del.icio.us client for Mac OS X.
The client downloads all your bookmarks and makes it available in a simple interface. Not much more functionality but it might receive some nice updates soon.