After developing several ASP.NET WebForms applications, I have to say that ASP.NET is a great framework. Despite the fact that my knowledge about the ASP.NET architecture is near to nothing, I was still able to develop something useful (I hope!). For the most part, my ASP.NET applications are simple, ad-hoc front-ends to some back-end functionality (see http://www.nrsr.sk/bin/net/nrozprava/ as an example). I didn't need to use any sophisticated custom controls; just a UserControl here and there in order to encapsulate some repeating functionality within a single application.

Sometimes, however, I needed to extend a built-in WebControl by deriving from it. You also can use this approach when one of the ASP.NET-provided controls "almost" meets your needs, but lacks some required bit of functionality.