This is true - within limits. Dropout rates do increase when the survey exceeds 15 minutes in length. Long surveys often require incentives, especially for MIS and technical professionals. Good medium for presenting product concepts, lengthy descriptions and visuals. However, complex graphics and visuals may require high speed internet connections or special player software to view.
Respondents can take the survey at their convenience.
However, some never get around to it. This could introduce a response bias. Less intrusive However, guidelines for sending e-mails are becoming very strict and spamming is now a legal issue. This is less of an issue with phone interviews. Respondents are entering the information themselves while viewing the question.