Most pools combine stale shares with invalid shares and provide a single stat.  Any pool reporting invalid shares separately also works.  Without knowing what % (if any) are bad shares (not just stale ones) the % doesn't really tell you anything.  


BTW: cgminer checks the nonce returned by the GPU with the CPU (only occurs once every 4 billion nonces so it is minimal CPU load).  If it detects a HW error it never submits it to the pool and increments the HW counter). cgminer isn't a magic bullet.  Sometimes you will have no HW errors and still have cards lock up but HW > 0 is a bad sign.  Likely means excessive overclock or a card about to fail.