Various app passwords vanishing on reboot

I thought it was just a fluke at first, since this never used to happen
before some weeks ago, but it's not: When I reboot, passwords configured in
apps such as Outlook 2007, Windows Live Mail, and Skype are blanked. In
addition, usernames and passwords on forms in IE (part of its Autocomplete
functionality) are also lost.

I think the common denominator with these apps is that they hook into the
system shell significantly, so this is probably related to Vista in general
in some way.

Any ideas? It's quite annoying to have to resupply the passwords so
frequently.

Vista Premium SP1