I have been using both stumbleUpon and digg for quite some time now, but recently started using them to promote my blogs – Tuubol.com. Digg.com gave me referrals for each article in the single digits whereas at stumble Upon I got hits in the hundreds. Now, the response from the bookmarks on stumble upon was quite overwhelming. Stumbleupon has helped increased the traffic on my blog from 20-30 per day to 400 in a single day.