Excluding the device statistics page already listing the (valid) results returned for each host, someone already asked for an amendment to show the filtered count on the Result Status (RS) page. ATM the work around is to first filter on errors/invalid and after visual scanning if multiple devices are involved, select a device to narrow it down (1st drop-down filter box).

Most probably you are familiar with the RS navigation, but just in case, here a link to the FAQ.

Added: With multiple or a great many devices on one account, the recommended tool is BOINCview. It logs all work-units, completed or ended in error and in the Hosts tab would show red colouration if any one device produces abort/errors.