LifeinAsia - 10:31 pm on Jan 10, 2008 (gmt 0)

I doubt most people know theirs. (My guess is that a lot of people don't even know there IS a +4 component.) I recognize mine when I see it, but I haven't committed it to memory. I have found that a lot of sites where I enter an address (e.g., for shipping or registration for online bill paying) automatically add the +4 component.

I agree that in some cases just the 5-digit zip code many not be sufficient for local search, but in many cases it should be.