Yeah it's one of those features that I read about and don't think about particularly much, but actually using it I eventually realized that it's a bigger deal to have it than I thought it would be. Love those sorts of "bonus" features that are a pleasant surprise!
I've been mistaking my work BlackBerry and my tablet for having knock knock... Very frustrating when I try it the second time and then realize what device I'm using.
I've been doing it to my husbands galaxy s2 phone as well Lol. It's so easy to get use to and also the back buttons, I forgot there's side buttons in the phone! My hands r small and the back buttons for me work great