no doubt, bookmarks can build backlinks. before that, we always use our main link of my web to produce bookmarks. Do you mean we should make some deep links for bookmarks too? for example, 30 % deep link, 70% main link what is your idea?
main link or deep link. Its about the news you are going to bookmark it. If your news targets the information from main link, give it main link.
Actually the deeplinks is the best. Since the main link is also included whenever you link build for your inner pages. What do you think?
Social bookmarking is the concept where one can bookmark the page of the site. So it depends on what is your targeted page. Home page is always there, so the keywords you are targeting for your home page, do bookmark of your home page using those keywords. And when you want to target your inner page, do bookmark your inner page. You can bookmark any page of the site you would like to.
Im agree with Rajuta. You should focus both the pages because google prefers best data on your site regarding user's point of view. So it is best to do social bookmarking for home page with deeplink pages. Cheers.....