That's awesome! I'll have to play with this, and suggest it whenever I hear the topic of coding interviews come up.
As a side note, if there's any chance of you being in the bay area this summer (Mtn. View specifically), I'd love to grab lunch with a fellow HNer. I'll be interning at Google starting early May and know a sum total of 0 people out in the area. If you're interested and possibly going to be around, my e-mail is on my profile page.