Learning about threading is fascinating no doubt and there are some really good resources to do that. But, my question is threading applied explicitly either as part of design or development in real-world applications.
I have worked on some extensively used and well-architected .NET apps in C# but found no trace of explicit usage.Is there no real need due to this being managed by CLR or is there any specific reason?
Also, any example of threading coded in widely used .NET apps. in Codelplex or Gooogle Code are also welcome.
That entirely depends on the application.
For a client app that ever needs to do any significant work (or perform other potentially long-running tasks, such as making web service calls) I'd expect background threads to be used. This could be achieved via BackgroundWorker, explicit use of the thread pool, explicit use of Parallel Extensions, or creating new threads explicitly.
Web services and web applications are somewhat less likely to create their own threads, in my experience. You're more likely to effectively treat each request as having a separate thread (even if ASP.NET moves it around internally) and perform everything synchronously. Of course there are web applications which either execute asynchronously or start threads for other reasons - but I'd say this comes up less often than in client apps.