Only time and testing will tell what will work best for you in this new medium. From there, you could move to measuring customer acquisition cost, which requires the customer to actually buy something. With response-oriented ad campaigns, you need to think of your ad campaigns with a process mentality because tracking doesn't stop at the click. If not, this will require you to know your business processes, information systems and customers. Today, many systems can track the clicks from the ad to the web site, including a web purchase.
Integration requires ad, web, email, database and transaction systems to be tied together.
Portability requires user profiles to be portable across the same systems and communication points. Advertising providers and web marketers need to find ways of bridging any gaps. The only effective way to target ads and information is to obtain data from the user. And going any further to track the customer beyond the ad requires you to tag and access each user profile. We follow two basic principles regarding gathering and using user data.