When writing a book, how important are the names of the characters to you?

very importatnt 

A book or any story is about people. Characters - including their names - are indeed a vital element.  No matter how good your plot is, or how adept you intertwine those subgenres if you are unable to establish your character, your book will definitely be a flop - readers will just toss your book away because they are not ready to figure out which character is which.

The names should have a cultural frame of reference, easy to remeber and woven in a plot that people can relate to.