PHP Class for sending a response to Flash
I have used PHP for a few years now, and here are my suggestions:

array_push() can be used to add multiple values into an array at once, but in your case, your pushing only one value in at a time which means you can use:

$ar[] = $key . "=" . $value

This should also speed up your code a little( What's better to use in PHP $array[] = $value or array_push($array, $value)?).

die() is normally used when there is an error. It spits out a message to the user. If you are using this code to just connect to a MySQL database then change die(implode("&amp;", $ar)); to  echo(implode("&amp;", $ar));

But honestly, you should be able to take out the respond() function if you are only using it to send an array to flash.

        // Connection could not be established
        if(!$this-&gt;con)
        {
            $this-&gt;response = array(
                "status" =&gt; "no_connection",
                "message" =&gt; "Could not connect to MySQL, try again later."
            );

             echo(implode("&amp;", $this-&gt;response));
        }