Most Effective Social Media Marketing tactics on Facebook and Twitter

Facebook and Twitter are the fastest growing networks in the world and are also the most popular amongst social media marketeers. A September 2009 MarketingProfs survey of business-to-business (B2B) and business-to-consumer (B2C) marketers shows some of the commonly used tricks as well as the most effective techniques of social media marketing on these two sites.
Most common marketing tactic used on Facebook was attempting to drive traffic to corporate materials through status updates, followed by friending customers. This tactic is one of the most difficult to follow and getting friends is very difficult to achieve.

But the most effective tactic for consumer-oriented companies was creating a Facebook application, which was done by less than one-quarter of total respondents. Both B2B and B2C companies also reported surveys of their fans as effective; fan surveys were the third-most-common tactic attempted. 

Twitter:
Again marketers using Twitter were also most interested in increasing traffic. Driving traffic by linking to marketing Webpages was the most common activity on the microblogging site, followed by driving sales by linking to promotional pages. But again, the most effective tactics were different.
B2C marketers had the most success with monitoring Twitter for PR problems (done by one-half of all respondents) and contacting users who posted negative comments about their brand (done by only 22.4% of total respondents). B2B companies also succeeded with brand monitoring, as well as with using Twitter invites for in-person events (the least common tactic of all).
source emarketeer
More on this subject:
Survey: what do Indian marketeers think about Social Media
Research: Social Media marketing not effective