Despite a sluggish economy, online shopping continues to show impressive revenue gains. Recent Forrester Research data suggests that online shopping will grow 17 percent in 2008, a far cry from what is happening in the brick-and-mortar world.

While this number points to increased interest in shopping online for both convenience and price reasons, it also highlights the growing relevance of subscriptions and other recurring revenue models as part of an online merchant's arsenal as an opportunity to grow the average customer lifetime value (ACLV).