You can get a short summary of filter's activity by typing:

    filter -s

For a longer summary type:

    filter -S

Or you can look at the log file itself, ~/.elm/filterlog.

You should regularly look at ~/.elm/filter-errors to make sure things 
are working.  You can automatically check filter-errors each time you
log in by putting the following in your .login:

    tail ~/.elm/filter-errors

Also you probably want to regularly delete filterlog and filter-errors so 
they don't fill up your disk space.  To get a summary of the filter log and 
clear it type:

    filter -cs