I agree with Chris. It is not a question of quantity but natural quality. Hummingbird and Penguin from Google had become smarter and and they quickly detect excessive link building campaigns. Google warned that it is now forbidden to cheat the authority of a site this way and strongly suggests indexing nofollow links. Social Network are strongly recommended such Google Plus, Pinterest, Linkedin, Twitter and Facebook are the strongest. Modern new types of directories are created and respects Paid Link and Link Scheme such as WISE. Many directories are penalized by Penguin for not meeting its new recommendations of Google. A natural baclink profile is now the best way to achieve your goals. Google will always follow a Nofollow link coming from a site that has a strong reputation and will now transfer "Trust" instead of Linkjuice.
