The New York Times recently reported on a study that found first-time online donors don't often return to make additional donations. The study was done by Blackbaud's Target Analytics.
I have to say I'm not shocked by the findings. It's pretty much what I've seen where I work. While our online giving has increased steadily over the years, it doesn't appear to be a giving medium which will over take more traditional mediums such as direct mail. What it has proven to me though, is that it's a good option to have available to your supporters, much like Mr. Smith of CARE stated in the article.