While everyone and their mother has an app these days, Google's decided to emphasize YouTube's mobile site as the wave of the future. It's faster and more feature-filled than the YouTube app; they even made a video to prove it.
This 90% figure means much faster starting up, searching and video loading. The video quality is also automatically optimized for your 3G or Wi-Fi network. If you are using a Nokia/Symbian 60 device, YouTube has provided the following compatibility list: