UIP is an effort to implement MVC design pattern for ASP.NET applications. MVC is good design pattern for every web application since MVC force you to build your application in layers, separate application flow from application block and usually decrease development time. MVC is also widely used with other developments tools and languages.
I agree that UIP implementation is far from being easy.

Furthermore UIP isn’t really MVC implementation since there isn't separation between controller and viewer. Anyway there are lighter implementations of MVC such as Maverick (http://mavnet.sourceforge.net/).