Social Bookmarking sites are really only helpful if you blog and can add your blog posts. That said social media in general is helpful to offline businesses because:
1. You can create a facebook fan page and drive your offline traffic there to build rapport, offer specials etc.
2. You can use foursquare which does not work for online businesses. It is location based and so you must have a brick and mortar location for this one to work.
3. You can use twitter for branding and to search and see who is looking for what you want in your area and then offer it to them.
These are just some of the possibilities. I do social media coaching all the time with local offline businesses. Check out the link in my sig file for more info.