I am a huge fan of Jakob Nielsen's work on web usability. He has a post out this week--"Four Dangerous Navigation Approaches that Can Increase Cognitive Strain"--that puts web usability into a system 1/system 2 framework. As I've said many times before, I believe that his research on web usaiblity has important implications for web survey design.
In his post Nielsen offers evidence for a principle I have long aruged is important in web survey design: unfamiliar answering devices and complex instructions absorb cognitive energy and distract from the key task of simply providing an answer to a question. I'm not going to rehash Nielsen's full post here, but encurage you to follow the link and have a read for yourself. You may want to pay special attention to dangerous navigation approach number four: "Fun" tools that become obstacles.