To add to Joanna's remark about heavy subjects taking a comma before
the verb (I assume by "heavy" Joanna means a long NP with lots of
embedded phrases and/or clauses): [1] this seems to happen when
the verb is BE, [2] E.D. Hirsch loves to put a comma there.
 
I just read an interesting comma splice in a novel last night. I'll
post it if I think to do so.
 
        --Bill Murdick