Here’s a real challenge – what makes up the true acquisition cost for a customer in a user-generated content site?  And what constitutes a ‘customer’?  Since revenue on sites like ours is driven by advertising and affiliate product purchases a ‘customer’ can be either a registered user (who can contribute content) or a visitor (who just looks at the content).

Customer Acquisition cost is made up of 5 major contributors in a business like ours – Pay Per Click advertising (Google, Yahoo), Banner Advertising, SEO Optimization, Viral Marketing Campaigns, and community management (headcount driven).  But these costs can drive both registered users and visitors.   Here are the relevant metrics from my view:

1) Cost per Registered User – monthly aggregate marketing spend/# of registered users

2) Cost per Visitor – monthly aggregate marketing spend/# of Unique Visitors

3) Cost per Action for Pay Per Click advertising

4) Cost per Action for Banner and Viral Marketing

These are interesting metrics to track and trend, but they beg some real questions.  How do we define an ACTIVE registered user vs. just a registered user?  Does it matter?  How do you factor in the value of items added as compared to number of registered users?  Is one user that adds 200 unique/interesting items (which positively affects SEO and visits) more valuable than a user that adds 2 items (or none, but blogs)?   Is there a way to segment registered users in a way to spend more efficiently to get the high value registered users?  Is that a smarter spend than just driving activities to get visitors who may drive more purchases and ad views/actions?

If you think about this question, it has important ramifications for most web 2.0 companies.  I’d be interested in understanding how others approach this question.