Apple has released MacBook, MacBook Pro Software Update 1.1 today which addresses a keyboard-freezing issue seen by many MacBook and MacBook Pro users under Mac OS X 10.5 Leopard:
This update addresses a responsiveness issue on MacBook and MacBook Pro notebook computers. Some MacBook and MacBook Pro systems may occasionally experience a temporary suspension of keyboard input which can last a minute or longer. The Mac OS X 10.5.1 update is required before installing the MacBook, MacBook Pro Software Update 1.1.
There has been lengthy discussion of this problem on Apple's support forums.