On newer cars, slowing down the alternator and water pump a little could probably be managed, although its not something you want to really mess with too much.

 

I have Neuspeed power pulleys for my 1.8t. The kit includes a smaller diameter, lighter pulley for the crank, power steering, and alternator. However, for some reason the alternator pulley wouldn't fit on my 1.8t (different bolt or whatever that holds it on). At idle, I have noticed that the headlights are dimmer. Also, the smaller pulley on the alternator does cause it to wear out faster (from what I have heard). But, I would not recommend using pulley(s) if you have an upgraded stereo system (like subs).

 

I believe the OEM pulley was compared to the OBX underdrive crank pulley and the OEM pulley weighed a whopping 4 pounds compared to OBXs crank at around 10 ounces.