Inspecting the status of a long-running COPY statement
There is not yet a formal facility for monitoring the progress of a COPY operation.  You can use the pageinspect extension to get an estimate of the number of rows, even uncommitted ones.  Assuming the existence of the table has been committed, and the table was empty other than the in-progress COPY, then you could use:

select sum(
        (select count(*) from
          heap_page_items(get_raw_page('pgbench_accounts', x))
        )
    ) 
from generate_series(0, (pg_relation_size('pgbench_accounts')/8192)::int-1) as f(x);


(This still assumes you are using the default blocksize of 8192.)