The recipient answers the survey by replying to the message which copies the text of the message to a compose message window. The survey is then answered by putting an X or some other character in-between brackets. Presentation of the survey is limited to text for many e-mail programs. Very high potential for the respondent to corrupt survey by deleting brackets. Very prone to processing errors once the e-mails are returned to administrator.
Respondents view e-mail text surveys as very unprofessional or antiquated.
There's a lot more, but we think you get the message about e-mail based surveys. The main problem here is losing respondents. Many respondents simply give up and fail to complete the survey. Inherent web server delays causing the respondent to give up. Potential to confuse cgi by using Back Button rather than a link on survey page.