Re:

Dan Langille <dan@langille.org> writes:
>          WHERE lastlogin between current_date - interval \''' ||
> quote_literal(i - 1) || '' days\'
>                              AND current_date - interval \''' ||
> quote_literal(i)     || '' days\''';

IIRC, quote_literal() puts single quotes around its result.  So you have
too many quotes there.  Given that you know i is an integer, you don't
really need quote_literal for it.  Actually, you don't need EXECUTE
here at all.  Why not just

    FOR i IN 1..MaxDays LOOP
        SELECT count(*)
          INTO r
          FROM users
         WHERE lastlogin between current_date - (i-1) * interval ''1 day''
                             AND current_date - i * interval ''1 day'';
        RETURN NEXT r;
    END LOOP;


			regards, tom lane