I was recently in L.A. and had an interesting discussion on the depth
and detail one should go to in developing characters for your
story.  I am a writer and also teach screenwriting.  My personal
preference is to write fairly detailed character descriptions for
my main characters, often going back as far as to who their grandparents
were and how the family arrived at where they are today.  Some very
respected writers told me that they write only a few paragraphs on each
of their main characters.  Just enough until their character "speaks" to
them.  Just for the heck of it, I tried the briefer biographies.  I didn't
feel that I had the kind of grasp on my characters that I wanted.  So I went
back to the detailed biography.
 
As in everything, you should go with what works best for you.  Nevertheless,
I am interested in what others do in terms of developing their characters.
 
Since there are a lot of new writers on this list I hope the responses are
informative.  At a minimum, I hope they will encourage new writers to focus
on building good characters.