E-Mail, Paid Search, Portal Advertising, Channels

How do you evaluate and segment customers who respond to e-mail marketing, paid search, natural search, portal advertising, shopping comparison sites, affiliates, and any other advertising channel?

Are these customers fundamentally "different" than other customers?

Do you treat these customers differently across various marketing strategies?

Most important, how do you evaluate the interactions that occur when customers respond to different advertising channels? For instance, should your e-mail marketing strategy be different for customers who respond to both search and e-mail, vs. customers who only respond to e-mail?