I dont se the big differece between Linkfarms and sosial bookmarking. The social bookmarking are offacause used by regular users and not only webmasters, and the pages ar usally dynamic. But the end result of sosial bookmarking is mostly list of links(and some descriptions) Is there any risk google will downgrade the importance of sosial bookmark links?
Even if G considers links from social networks to be less important in the future, you shouldn't worry about it. Any type of link is good, and low importance links is ALWAYS better than NO link.