Drupal is one of the most popular open source CMS'es, but it's not geared towards complex surveys. I think that both Drupal and Limesurvey would benefit from a Drupal-Limesurvey integration module.

In many surveys in organisations, it's considered important that each respondent only replies once. Therefor, you use a token in order to allow each respondent to fill in a survey only once. However, it is now possible for a respondent who has saved his/her form, to start a second. The record created by the first, unfinished form is not removed from the database. As it is an anonymous survey, it's not possible to identify this record. If you want to guarantee the uniqueness of each respondent, there is no other option but to throw away all unfinished records, in which case you also remove records of respondents who had other reasons for not finishing the survey.