The WiFi dongle will not affect the quality of of I-player / Youtube, The weak link in the system will always be you broadband speed, The Wifi link is rated at 54Mb/S so even if the link was only running at half this it would still keep up with a 24Mb/S broadband link (which is still quite rare in the U.K). The bit rate required for I-Player / You tube is almost 10 times less than this figure