For me, a clip in the following video demonstrates my understanding of the irimi principle.
It's a nine minute video but the relevant section I'm referring to occurs only in the first 1.5 seconds. Blink and you'll miss it! You'll certainly have to replay it.
http://www.youtube.com/watch?v=EmSnb-Es2vI
(Notice the 'shita kara ue' nature of the movement).