Reddit has literally changed the way I research and surf the web. So much useful information there, (so long as you are in the subreddit that is topical to you) Sometimes it can get a bad wrap, but I feel like I've made a lot of friends on there, and historically speaking, am usually the first to find out a lot of trending news. I prefer reddit much more to sites like 4Chan.
Edit: I forgot to mention you bringing up Digg brought back fond memories!!