Many marketing executives in large companies think of social media as a pitfall to avoid, but not Andy Lark.Lark is Commonwealth Bank's chief marketing and online officer, and, at last week's AB+F Mortgage Innovation conference, he outlined a number of marketing initiatives the bank has launched using social media.CBA staff monitor Twitter to look for references to competitors. If they find someone complaining about their bank they send a tweet suggesting the disgruntled consumer consider an alternative offering from the CBA.Results from this activity have been encouraging enough that the bank now has a revenue line for its Twitter activity.Lark said social media allows people to do their banking at any time they choose. "Banking is now something you do while you are doing something else," he said.This encourages people to personalise their banking activities, which can be very valuable for marketers. For example, instead of opening a savings account, a young person is more likely to open a "holiday account" or "car account".With this information the bank can send more accurately targeted marketing messages.The bank has a high rate of transaction-account customer acquisition using special offers on Facebook."Using Facebook to run a campaign we get in seven days what we get in a month using old media," Lark said.The bank is also using social media internally. Lark uses the enterprise-based social network, Salesforce Chatter, to encourage staff at all levels to send him their ideas.