The privacy issue here is interesting.

It makes sense to guarantee anonymity. Participants recruited personally by company founders may be otherwise unwilling to report honestly (for example). For health related studies, privacy is an issue for insurance reasons, etc.

However, for follow-up studies, it seems important to keep earlier records including personally identifiable information so as to prevent repeatedly sampling from the same population.

That would imply that your organization/system needs to have a data management system for securely storing the personal data while making it available in an anonymized form.

However, there are privacy risks associated with 'anonymized' data as well, since this data can sometimes be linked with other data sources to make inferences about participants. (For example, if participants provide a zip code and certain demographic information, that may be enough to narrow it down to a very few people.) You may want to consider differential privacy solutions or other kinds of data perturbation.

http://en.wikipedia.org/wiki/Differential_privacy