Just few days ago, I have created accounts in nearly 600 different social bookmarking websites. Then i bookmarked a website in all 600 social bookmarking websites account. Then i create rss feed and submit to feedlisting and feedagg. Just after 2 hours i check each social bookmarking account profile url [for example, Code: http://digg.com/xxxxxxxxxx in google to verify which is indexed. I found digg account is already indexed by google and all rest other feedlisting link is indexed by google. So in my view Google gives more value to Digg than other social bookmarking website like delicious, plurk, stumbleupon, reddit, mixx, folkd etc..