Jennie Yorke and Richard Turner from ActionAid have a great presentation on Slideshare. It shows how the charity's approach to recruiting child sponsors has changed over time.

In the three years up to 2005, 70% of all child sponsors were recruited through three channels. Today those routes generate just 29% of all sign ups.

A massive 30% now sign up online, primarily as a result of seeing offline fundraising materials.

It's only a few slides, but shows the clear benefit of integrating communication channels.