Apparently, I disagree with most people here.
I find that 5.1 is worth getting.
However, not to the exclusion of a good 2 channel stereo system. (First things first of course!)
I find that watching DVD's and listening to them in stereo is distracting, as you have to crank up the sound to get past all of the music, special sound effects and other crap, that is added from the front and rear surrounds, just to be able to listen to the dialog.
By having a center channel, (that pretty much only carries the dialog), I find I can listen to the movies easier without having to listen to the dialog through the extra music and special effects. (To me, the music and special effects coming through the surround speakers are mainly to augment the movies (and the dialog), not to dominate the sound.)
Now, if I had to choose between a good stereo system and no 5.1 for video, or good 5.1 and poor stereo system, I would pick the good stereo system everytime. (However, you are definitely going to miss the 5.1 soundtrack.)
I waited until I had my stereo built up to a decent level, and then added a second HT setup in the same room, which is a decent 5.1 setup, but in no way, shape or form competes with my stereo system. (I probably spent a 10:1 ratio between my stereo and my HT setup.)
Life is full of tough choices!
You need to make up your own mind which is more important to you, at this point in time: Music or Video?
Good Luck!