Well, think about what you want to do. You want to set $foo to $GET['foo'] IF $GET['foo'] contains a string. Otherwise, set it to 'Default.' So...
if ($_GET['foo'] != '')
$foo = $_GET['foo'];
else
$foo = 'Default';
There's a shorter way to do this, with a bit of syntax inherited from C.
$foo = $_GET['foo'] == '' ? 'Default' : $_GET['foo'];
Also, you should probably use $REQUEST instead of $GET unless you specifically only want GET variables. $REQUEST contains all variables supplied by any input method, POST or GET. You could also do if ($GET['foo']) since a blank string returns FALSE in PHP. However, if your variable could take on another valid value that PHP considers FALSE, e.g., 0, then that'd be a bug.
