Brand new MacBook Pro with Retina display - Mail, Preview and App Store freezes on launch
Found out what it was.

Ink > Write Anywhere was enabled, when it shouldn't. As soon as it was disabled, the affected Apple apps started working again.

I thought it was something to do with the Wacom tablet I bought, but couldn't find any connection. Now I know it was Apple's own Ink software. Maybe I shall report it as a bug.