While much of the excitement in the .NET community is around MVC, many of the applications out there continue to be in webforms. If for no other reason, you should continue to learn webforms so that you can convert applications over to MVC.
I've been working on MVC since the 1.0 RC, but no matter where I have gone in my consulting work, if there is .NET you almost invariably will see webforms. In fact I would dare say in the enterprise the majority of applications are still in webforms.
In my view MVC is a much better platform, and webforms will probably not be supported eventually (although Microsoft continues to say it will). Still how many of us said that VB6 will go away and got burned when we find an ancient bug and have to spend days just figuring out how things work?
We're still years away from having webforms be phased out completely, and you don't want to restrict what you can and can't do because you decided MVC is the only way (your company may not want to spend the money on converting their mega-spectacular webforms app because you don't like webforms).
More knowledge never hurts, but ignorance can burn you.
