I do like social bookmarking for some clients as a way to build one way inbound links, but I feel that there are better ways for other clients. Social bookmarking works great to build links for website and blog content that is timely, well written, and a hot web topic.
For the majority of business sites that focus on their own services, more mundane topics (although they could be of interest to a specific audience), social bookmarking may simply be too much trouble for the results that it generates. One big caveat is that if you have a well developed social bookmarking profile and many followers, you may have much better success than just opening an account and starting to bookmark away.
I find that if you are going to really invest time in building links a faster more sure way is to write article pieces and syndicate them on newsletter and content sites for others to grab while keeping in your bio block and link information. Even better is to see if you can guest write for a professional organization in your industry. The key here however is that any article you provide must be informational in nature and not focused on your own particular services.
Do I feel that social bookmarking has a place? Yes, absolutely, but it is labor intensive and best used for certain topics, content, and specific clients.