If you're wondering what the performance impact of using the @ operator is, consider this example.  Here, the second script (using the @ operator) takes 1.75x as long to execute...almost double the time of the first script.

So while yes, there is some overhead, per iteration, we see that the @ operator added only .005 ms per call.  Not reason enough, imho, to avoid using the @ operator.

<?php
function x() { }
for ($i = 0; $i < 1000000; $i++) { x(); }
?>

real    0m7.617s
user    0m6.788s
sys    0m0.792s

vs

<?php
function x() { }
for ($i = 0; $i < 1000000; $i++) { @x(); }
?>

real    0m13.333s
user    0m12.437s
sys    0m0.836s