Normally Traffic from Search engine is Best , Referral sites ( digg, stumble ) usually not able to give you Good Earning , Try concentrating on Search Engine Traffic which is Best For you Saad
well i am getting zero traffic for my blog from search engines because of the competitive niche, i get only traffic from social bookmarking sites and direct traffic
Thats not a problem what people actually mean by saying social bookmarking sites is not good is because these ppl click the ads very less almost nil
I have also a questions that, its ok if lot of traffic come from Email, Orkut, Facebook ( or other related to these), youtube.