That's the idea behind Nextdoor, a new web thingie that's been in beta for a while but goes live on Monday. You register your neighborhood and then invite your neighbors to join in, see who has an edger to borrow, who has news on lost pets, any crime info to share. You have to live in that neighborhood to be a member of its network (no dreamily joining the West Village, Nebraskans) and you have to use your real name.
My own neighborhood is attempting to do this by email after some recent break-ins and a missing cat but it's meant emails with 50 names and lots of bounce back emails. Kind of a mess. Maybe Nextdoor is the answer.