I agree that one should not deceive their employer. At the same time, if their employer does not notice a drop in productivity/performance from the employee, what's that say about that company's ability to actually measure employee performance?

I think a lot of companies have poor project management & employee performance measurements, so half the time, people only have half the picture or don't know what the heck people are supposed to be doing and if that's actually getting done. That only becomes more complicated when projects are abandoned and/or requirements shift every quarter.