For me, stumbleupon just generated lots of traffic. I've been stumbling my posts for a good month or two now and usually only find 2-5 visitors from there. But a few days ago I had 40+. Not sure how it happened.
Right now, Twitter is my only means of driving traffic to my blog. My blog is VERY new, but I've been on Twitter for quite a while, networking with other people in the horse industry. My twitter address is http://twitter.com/MoonshadowFarm
I also have many Twitter followers that I got through my husband and his blog, www.entrepreneurialdaddy.com
Those are the ones that have given me the most comments so far. Even though my blog is horse and mama centered.
I have found that my connections on Twitter have helped me out in many ways. If you're careful who you follow, you can have a strong group that genuinely cares about what you do. Then, they are more willing to help you out!