DiggLicious gives you live updates of what's going on both digg and del.icio.us. 

...you can observe a live view of the action on these two sites without having to reload your browser. If a site interests you click on it to check it out, then return here and use the handy links to go directly to del.icio.us to bookmark it or digg.com to digg it!

It gives a nice snapshot of the action going on within both sites, but of course, doesn't replace either of them.  Nice tool.