..the answer - never.  In fact Marketing and Selling have become so intertwined in today's inter-connected world that one should really challenge why we still need separate departments as still exist in so many organisations.  Today, every Marketing opportunity is a Sales opportunity, and every Sales opportunity a Marketing opportunity.  Marketing is more and more about a two way communication - and that communication is a means to sell.  And on-line sales is the best way to market added features and additional products.  Every organisation needs to understand all the interactions that occur between their customers/consumers and themselves - and they way those interactions can lead to a sale.  The classic marketing acronym AIDA - Awareness, Interest, Desire, Action - is still a relevant path to action, but whereas before each step was associated with a separate step (eg Awareness is raised through Advertising, Interest through Promotion, Desire through PR and Action through Direct Selling), in today's inter-connected world, the journey to action is likely to be more rapid and interdependent.  Critical at each step is communication - and even more importantly, real time dialogue.  How are you connecting to, communicating with and even talking to your customers and consumers at each step of their buying process using multiple media to enable you to do this?  It is a challenge which few organisations yet fully understand.