If you are planning on running a large stereo or ton of electronics, I would suggest leaving the stock alternator pulley on to make sure your charging system works correctly. If you are at all worried about charging problems, just leave the alternator pulley stock and you should have absolutely no problems. When you do put the alt. pulley on, the lights tend to dim at night when you come to a stop. To compensate for that, many tuners will up the idle speed.
I ran around with my underdrive pullies on my 1998 CV for over 75k miles and had no ill effects.