If you had to choose a single, dominant trend in 2008, it is "accountability". And now, recent economic challenges have made it the supreme measure of all marketing media.

A recent survey of members of the Association of National Advertisers found that 53% were cutting budgets in response to the downturn, and that 40% were altering the marketing mix to lower cost channels. In this case, “lower cost” is a direct translation for “online”.

Planned advertising expenditures in traditional media – newspapers, magazines, network TV and radio – are down by double digits for 2009, according to Nielsen. But the online categories - email, search, Web and social media – continue to grow and grab a larger share of marketing budgets.

And of the four, that old stalwart – email – is leading the pack. According to a 2008 survey by the Direct Marketing Association, email is the online marketing tactic used most today vs. three years ago; even more than search. It begs the question, why?

A big reason is accountability. As the most measurable of all media, there are few mysteries in email campaigns. Marketers know what they spent and what they got in return. It’s the reason they know that email delivers high ROI for both acquisition and retention.