How effective are they, from sites with 5,6,7 8 PR? How many backlinks does it take to become relevant? Also which are the best to post to?
It depends on your niche. I have mostly Occult sites, which never get anyplace on Digg, as they do not have a category for such things (Unless that's now changed, in which case, someone please let me know). Stumble works wonders though, as there are a lot of pagans out there that adore SU. Personally, I love Delicious, but then, it's done little to nothing for my site.
I'm thinking the pagerank from most of the (mainstream? top?) social bookmarking sites isn't really that helpful. The traffic and exposure is what it's all about in my opinion.
I have had great results with social bookmarking sites, specifically Digg. Submitting quality articles to them has allowed me to rank on the top 5 in Google for highly competitive keywords. The secret to achieving this is to name your post carefully (on Digg) including the keywords which you're looking to rank high in. Write a well thought out description of your article, what it means to you, and what it offers others. Once your article has 9-15 Diggs your Digg article will actually rank high in Google, because Google loves Digg. When they click the link they are obviously taken to Digg with your link in their face, and they all click that link. Using this method has helped me to generate a ton of traffic in a very short period of time. I'm not sure if it has helped my page rank, but it has definitely helped with traffic, and traffic is much more important than PR (IMO).
SU brings in traffic sometimes, and whenever I get traffic from there, bounce rate is generally low. Digg does not do any wonders for me. Others are just okay.
I had a political blog post go to PR 5 for a while with just some links from Reddit - and the spillover blogging that people did about the article. It went back down to 2 the next time around but it ranked up around the top financial websites for international and energy related keywords for a while. Most pligg sites and smaller bookmarking domains hardly even get all of their links indexed. If its nofollow you'll won't even get direct traffic unless you have a good match between the community's interest and your own niche.
Frankly at times I have received a lot of traffic from one or another social bookmarking sites but that has never contributed to people buying things on my site or even increasing my adsense revenue I prefer using these sites for link-baits and to get stories indexed quickly.
There are also some other ways of solidifying social bookmark links, I'm talking aside from the traffic now for which I've had the best experiences with Stumbleupon. Oftentimes your submissions on major bookmarking sites such as digg will not necessarily get indexed especially if they don't receive many diggs/votes. What can work to at least make them relevant in terms of ranking is bookmarking those submissions on the more generic bookmarking services such as furl,delicious,etc. then grabbing the rss feeds from those accounts and plug them into a social feed aggregator such as lifestream.fm - this gives you backlinks to your post/submission on the heavyweight social site which in turn will increase the chance of google indexing and weighting the submission.
That's an excellent advice. I remember Jim from this forum had given the same advice and I have been following it after that. But still SB links are not as useful. Specially the traffic. It never converts
maximum Bookmarking site use nofollow tag so Google does not count that backlinks, only few sites give Google backlinks
Sounds great, but am I building castles on clouds? How do I get the lifestream.fm page indexed without creating reciprocal linking from my bookmarking accounts? (I'm kind of joking, my lifestream page has its own RSS feed so I can just keep running deeper down the rabbit hole of backlinks & indexing)
social bookmarking sites is only good for traffic and this traffic converts very poor. also you have to participate on this SB sites if you wanna see some good results. time consuming. good for traffic not for money