While I understand that most of the time people use 3rd party applications for this; I use my wiki to store my accounts also because it is so darn handy. And when I ran an IT department we also put this stuff into the wiki. Normally I use a table:
====== Passwords ======
| URL | Name | Password |
|-
| http://mydokuwiki.com/| myname | mypassword |
|-
| http://mydokuwiki.com/| myname | mypassword |
|-
| http://mydokuwiki.com/| myname | mypassword |
|-
I tried to use the DokuCrypt function to protect the passwords but it doesn't work on the latest version.
Again, I can not stress enough how useful it would be to have an easy way to store 'confidential' information into a wiki because they are so really darn useful for CMS.