This is really interesting, thanks for the list, indeed social bookmarking. Social bookmarking is an excellent way to create quality backlinks to your articles,
You have to increase you fan page, like pages, comments on pages, add more connections and make sure to post interesting content that would basically add more loyal customers.
Doorway pages are web pages that are created for spamdexing. This is for spamming the index of a search engine by inserting results for particular phrases as explained by wikipedia.
I'd go for article submissions. Social bookmarking is an excellent way to create quality backlinks to your articles, which is always a excellent way to gain the attention of search engines and increase your pr.