I was having a problem in Vista that Outlook 2007 would always ask me for my password when it opened, or when changing folders after being open for a while. It would have the password filled in and the "Remember Password" checkbox would be unchecked, so I would check it and hit "OK". But it wouldn't remember- sooner or later, it would come up again. It was really annoying. It would prevent Outlook from being able to "Send & Receive," failing silently until I switched folders, which would bring up the password prompt again.
I assumed the problem was this, and that Microsoft hadn't gotten around to fixing it for Vista. But apparently, this is the actual solution. Thus far it seems to work. Woo hoo!
UPDATE: It may work temporarily, but it doesn't stick. D'oh!
UPDATE 2: Microsoft Office Outlook Connector (indirectly) solves the problem