Some people think such backlinks are a waste of time, and others actually think they will hurt a website. However, Google has said that quality directories can help a website's SEO, though not massively. Nonetheless, perhaps a lot of them would help out. I'm not sure what they said about social bookmarking.
I always hear that social bookmarking is not very good for gaining your page rank, but it is still good. I'm pretty sure that it's safe to use social bookmarking in SEO your page.
Directories are no more important these days as Google considers these sites as spam with very less content. Only a handful of directory sites are crawled and indexed by Google.
Social bookmarking can be a great way to drive massive traffic to your site, but you need other people to actually share your site on them. Self-promotion is very strongly discouraged on many of them, and getting caught doing so can result in your account (and eventually if you keep making new accounts to get around it) your domain blacklisted.
Directories are not really worth taking time to work on adding your site to, though. People don't use them anymore and they do not help your SEO.
Directories have lost their importance in today's SEO. Even Google only considers few social bookmarking sites for indexing and crawling like Diigo, Bibsonomy, slashdot, reddit, stumbleupon, etc.
Directories are not important now but some bookmarking sites are good. Old SEO may work for short runs. You need to aim for long terms results. Google has indicated that it will ignore such low-quality backlinks.