With ASP.NET MVC 3 to be out soon, there are still many developers confused on whether to use MVC or the standard Web Forms UI while building their own custom ASP.NET web applications. I know this has been debated numerous times in the past but let me write on this topic in brief. It would be best to understand this excerpt from the man who created the ASP.NET platform, the great Scott Guthrie:

a) Web Forms and MVC are two approaches for building ASP.NET apps. They are both good choices. Each can be the “best choice” for a particular solution depending on the requirements of the application and the background of the team members involved. You can build great apps with either.  You can build bad apps with either. You are not a good or bad developer depending on what you choose. You can be absolutely great or worthless using both.

b) The ASP.NET and Visual Studio teams are investing heavily in both Web Forms and MVC.  Neither is going away.  Both have major releases coming in the months ahead.  ASP.NET 4 includes major updates to Web Forms (clean ClientIDs and CSS based markup output, smaller ViewState, URL Routing, new data and charting controls, new dynamic data features, new SEO APIs, new VS designer and project improvements, etc, etc).  ASP.NET 4 will also ship with ASP.NET MVC 2 which also includes major updates (strongly typed helpers, model validation, areas, better scaffolding, Async support, more helper APIs, etc, etc).  Don’t angst about either being a dead-end or something you have to change to.  I suspect that long after we are all dead and gone there will be servers somewhere on the Internet still running both ASP.NET Web Forms and ASP.NET MVC based apps.

So as the man himself says, ASP.NET MVC is NOT a replacement to the Web Forms, but rather an ALTERNATIVE. Some people who are really comfortable with web forms, might not want to learn the new MVC option, considering the learning curve involved. Developers who are comfortable with the MVC architecture would love developing MVC apps in ASP.NET using ASP.NET MVC. So essentially its a choice, based on your own personal taste. None of these options are "bad", and as Scott mentioned, you can build great web apps using both!