What is a dissimilarity between digg.com, mixx.com?

Do you think that digg user are rapidly changing their tool with Mixx.com? [ In trafficestimate.com ]   What is a dissimilarity between Digg.com, Mixx.com? Social network system (like twitter.com) is a good story and popular system in web2.0, so Digg.com start up friendship system like twitter.com. Mixx.com support social network system, too. They are similar in machine don't gather popular article(url) but human submit his own url or interested url. In terms of blogger regard their post advertise as important, maybe not bad.