As the title says, are they REALLY worth it? Looks like to me to get anything out of them you have to be a bit active? What benefits apart from maybe minimal traffic does social bookmarking sites have? I have my blog submitted on some but i get NO traffic from them, I am thinking it's because I am not active?
They server as a good backlink source, and if you post good content and make the digg homepage, you will definitely see some nice traffic coming in. So yes, I think they are worth the hassle. (Some are anyway)
Iused stumble upon and other social bookmark sites and getting lots of traffics.. here is my report. Social Bookmark and web traffic
They do not work the same for everyone. You have to look at each of them as individuals, and read the personality of the site. For instance Fark will do you no good if you are not writing Humorous or political stuff. Stumble is good for numbers but not for buyers. Technorati has never done anything for me at all. Digg is good if you break a story, or have completely original content. ..and so on. So they will not work for everyone the same way.
It's all different for different topics and people... the ones who are active also have a bunch of people following them already who will automatically vote for whatever they submit... but submitting to them can definitely help you with SEO and search engine traffic too so like I said, it all depends...