Since I installed the SP1 update for Outlook 2007, now my IMAP account's
INBOX and Sent folders disappear from the "Favorite Folders" every time I
close and re-start Outlook.
(Other accounts' folders do remain in place correctly, including Outlook
Connector (live.com) inbox and my local PST-file's POP3 inboxes.)

p.s., I see this is a previously discussed problem... Office Discussion
Groups' search feature failed to show me any of those postings before I
posted my question. (sigh) To be specific, I typed this into the search
control inside Outlook: "IMAP Favorite Folders disappear when restarting
Outlook after SP1 update"

SO, NOTE TO MICROSOFT: Please check both problems, the Favorite Folder
problem and the forum-search failure.