Internet marketing used to be a blindfolded shot in the dark. Now, you can stay front-of-mind with your most narrow markets. Technology has gotten pretty "smart" over the last five years.
Which demographics (or combination) matter most in your marketing efforts? Is it a specific age range, gender, location job titles, income... or do you simply want to communicate with those who visit your site?
Remember shopping for an orange pair of boots a few weeks ago? Didn't you think it was ironic when you started noticing ads for orange boots during the next few days? #ThatWasNoCoincidence