My experience re: the first item is that turning ON Cached Exchange Mode causes the behaviour you're seeing-- not turning it off. That's odd.
I have a particular Customer site where all 17 users in the office have the mailboxes of the other 16 users open (in an ugly "Outlook mesh topology") running Outlook 2003. Their "former prior IT provider" configured it that way to facilitate calendar sharing w/o having to use the "File / Open / Other user's folder..." option (and, apparently, they never noticed the "Favorite" behaviour that was added in Outlook 2003 to keep recently-opened calendars in the user's "Other Calendars" list). (They're not running Cached Exchange Mode, either, because they complained that they were double-booking appointments when secretaries would access the Principals' calendars simultaneously and weren't looking at "live" data. I can't say I ever personally witnessed that happening, but turning off Cached Exchange Mode seemed to make them happy...)
It's working fine for them. All the mailboxes are hosted on the same Microsoft Exchange Server computer on their local LAN, however. I'd suspect that Outlook might burp and sputter a bit if you were opening mailboxes on multiple Microsoft Exchange Server computers.