Let me begin by asking what kind of writer do you want to be? Most professional authors would recommend avoiding the English/creative writing major unless you want to write literary fiction. In fact, many literary fiction writers would also tell you to avoid the English major. Here is the catch 22:
If you are very committed to being a writer, then you will write a lot in your free time. In most cases, doing so will give you plenty of training in the physical act of writing, especially if you are constantly reading in the genre you want to produce. The English program will give you a little bit of refinement, but not much. Re-read 42's post--he said a lot of very good things. The thing about most English programs is they will teach you very little about writing itself. Most of your classes will be literature classes, and you will learn to critique and analyze texts. A good critic does not make a good writer, and vice versa.
So, what will an English program give you? Well, if you are absolutely terrible at prose and mechanics, you will be forced to learn to better yourself. You will learn some things about revising and about publishing--though these tend to either come very early in the program or very late. The biggest problem is that if you spend all your time on English, you're left without anything to write about. If you want to continue in academia, the English program is good. If you want to go into professional editing, it is an all right major. But if you want to be a writer, other areas will do you better.
For instance, a history major will know a lot more than an English major when it comes to writing fantasy. Someone in the sciences will have a better grasp on science fiction. Mainstream fiction usually has a catch too--like lawyer novels or psychologist novels. The things you need from an English program--such as some creative writing classes for workshopping--can be gained through a minor, or from simply taking classes without either major or minor. English departments tend to be very non-exclusive.
Personally, I didn't know any of this when I started. I chose English because I thought that's what writers did. It hasn't done me any harm, but I'm not certain I feel that I've learned much that is of use to me. In reality, the most it did for me was allow me to get a Masters, which will in turn allow me to get a PhD, which in turn will let me teach.