The Zone System was originally used with B&W film photography. With colour digital photography, though, couldn't you get much the same results by keeping an eye on the histogram? I think I might have missed the point, so let's ask: would I gain anything by learning to use the Zone System with my DSLR?
The wikipedia article on this has some good information. Basically, yes, it is probably still worth the time to learn the system, but you probably won't use it in it's original form. The Zone system will tell you what the exposure and dynamic range should be, and the histogram will tell you what the exposure and dynamic range is. The benefit is in knowing the difference between the expected and actual results, which allows you to adjust to get what you want.
The complete zone system is a method for controlling the contrast in photography by adjusting development of film versus final print contrast using an enlarger and paper printing. Aside from it's historical significance in the history of photography, it has no bearing in digital photography. Contrast and tone value, to some extent, is independant of camera exposure values. All one really needs to do today is keep the highlights from blowing out, beyond that all the variables ansel had to control so tightly, are simple sliders in post processing.