There's also a very accessible search function, with thumbnail support and expanded video details before you open a video. The quality on offer here is far better than the official client, and that's reason enough to pick this up. Even without the free trial, it's great value at 79p.
In an earlier version MetroTube was known as LazyTube. The update to version 3.0.0 sees a name change and a near total rework of the application. As such it's fair to say MetroTube is effectively a brand new application. There's no doubt it is currently the premier way to consume YouTube on a Windows Phone device.
And a hat tip to My Nokia Blog for the original story.
PS. [from Steve] HTC Windows Phone handsets already have a HD, high quality YouTube application built-in, of course, so MetroTube is probably more for the Nokias, Samsungs of this world, etc.