Make no mistake: I love my cell phone, I love being connected, but I am not a rude person. (Or uh, I try not to be.) I like to think I know when to quit, and save for some especially dramatic situations, I know when to silence and say I'll call back. I'm pretty sure you guys are on the level too, since you reacted smashingly to my new Cell Phone Rant group!
For those moments when some people need more than a meaningful look, you could always put up a sign. Before you balk, check out how clean and classy this No Cell Phones sign from Etsy is. I wouldn't necessarily have a place to hang it in my home (except maybe in the bathroom as a goof), but if you have a business, or are a librarian, or diner owner, let the sign say what should be common sense for others.