I installed my pulley set about a year ago. It is one of the two piece sets for the crank and alternator that I picked up used off Ebay. Link to this particular set:
http://www.gofastbits.com.au/index.p...ub_option=2001
The install was pretty easy and took me about an hour or so going slow and figuring out all the points that I needed to loosen for the tensioners. If you are thinking about doing this install you need a long breaker bar, regular ratchet set, shallow 22mm socket, 24mm socket, an impact gun and a buddy.
There is a huge difference in weight between these pulleys and their stock counterparts. They are of very high quality, and seem to work very well.
So far I have noticed improved throttle response. I don't have a lot of accessories in my car, but I haven't noticed an problems with loss of power or anything.
I am totally sold on Go Fast Bits products. They have a variety of pulleys to choose from including a non underdriven one.