Hi. Stumble Upon, Digg etc do provide backlinks to your site. Stumble upon gets you quite a few visitors providing you put in the right tag and yes, the more likes would mean more views though of course many visitors may not choose a preference by clicking like/dislike.
I use stumbleupon to promote my hubs, its a good bookmarking site. You can also put them on shetoldme which has adsense revenue share like hubpages. You can get adsense from putting the bookmark on to your hubs/site.