Techcrunch report on the (free) BreathBird twitter app for the iPad.
BreathBird employs the well honed concept of ‘scanning‘ that’s been used for alternate input selection on software like on-screen scanning keyboards for years and applies it in a fresh way to this iPad app, using breath as the trigger rather than a switch.
I’m unaware of any other apps using the scanning keyboard input method, so this may be a first on the iPad.
Taking the concept further… how about using the front-facing camera of the iPad 2 to ‘view’ and sense a blink as the trigger. Now there’s a project.
life tools 
This program really is good, I was amazed at how functional it was!