I have to admit that while I'd read a few things about Cairngorm, it still seemed murky to me. The fog cleared when I read chapter 20 in Developing Rich Clients with Macromedia Flex. It's interesting that although the book predates Cairngorm, its description of techniques that Cairngorm later embodied made things click for me.
This book has cleared some other Flex fogbanks for me, too. I think it's truly a gem that's slipping into the sands of time.
Caveat emptor: the book is based on Flex 1.0/1.5, with ActionScript 2.0 -- you'll need do some translation as you read it, and some things simply no longer apply. But I think it's still well worth the money.