A strategy that works well for me is to create one manual web 2.0 property a day, or 5 within a week, etc. MANUAL. I will post anywhere from 3-5 articles on each web 2.0 property (blogger, tumblr, weebly, yola, wix). Since I am a native American, writing high quality content comes more natural to me than it does for others, so I always write it myself. Out of 3-5 articles posted on a Blogger or other Web 2.0 - only 1 article will feature a backlink to my website. I make it look as natural as possible, as this is the only way to guarantee the backlinks stick and don't become a waste of time.
Diversity is important though, so don't do a bunch of Blogspots, do other ones too. Squidoo, Hubpages and Wizzley are also great for getting backlinks, so switch it up. There is no magic number, just make it look as natural as possible. This is what works for me and hopefully it'll continue to work as Google gets tougher on certain SEO practices.
