Social Bookmarking has a real place integrated into your Search Engine Marketing (SEO) strategy:
You’ll get backlinks – these are the links back to your website that drive Page Rank and traffic.
Bookmarking a page or a new blog post on your site will get that page indexed more quickly by the Search engines
Most social bookmarking sites allow you to use tags. List your target keywords in these tags and this can help your ranking for these keywords.
Author Matthew Simmons