I can cite ways in which telephone-based and mail-based survey research have declined in efficacy while increased in cost, time, and headaches all day. These methodologies are still appropriate for certain types of marketing research studies, but when we can construct a solid online-based solution, we strongly recommend this route.
On occasions where I want to find data to support rationale for recommending an online survey methodology for a particular target I consult a number of regularly updated sources. One very helpful source, especially when the targeting is based on demographics or life stage, is the Pew Internet & American Life Project. I’ve referred to their 2005 research on Internet usage many times, but I expect to refer to their newest report on generational Internet usage in the coming weeks and months.