Password Security: What Users Know and What They Actually Do posted on Bruce Schneier's blog.

The finding that participants in the current study use such simplistic practices to develop passwords is supported by similar research by Bishop and Klein (1995) and Vu, Bhargav & Proctor (2003) who found that even with the application of password guidelines, users would tend to revert to the simplest possible strategies (Proctor et al., 2002). In the current study, nearly 60% of the respondents reported that they do not vary the complexity of their passwords depending on the nature of the site and 53% indicated that they never change their password if they are not required to do so. These practices are most likely encouraged by the fact that users maintain multiple accounts (average = 8.5) and have difficulty recalling too many unique passwords.