I should just give up on kmail.
After enabling 'disconnected' for my google imap, I see a really nasty behavior.
When I try to open a folder, I get a spinning graphic effect on the folder name.
This is (probably) what causes X to use 100% cpu (nvidia driver).
That's really helpful. Because the computer is busy, it's taking a while to
update, so kmail helps out with a graphic that uses 100% cpu. A positive
feedback loop.