Some of new features:

• Support for async unit tests (.NET 4.5 or Async CTP), for tests returning Task
• Support for generic theory methods
• New assert: Assert.Equal<T>(IEnumerable<T>, IEnumerable<T>)
• New assert: Assert.Equal<T>(IEnumerable<T>, IEnumerable<T>, IEqualityComparer<T>)
• Added parameter names to the display names of theories
• Improved assertion messages for Assert.Equal when called with collections

more at http://xunit.codeplex.com/releases/view/77573