We had one put in when we built our house. We LOVED it, until we realized that the water was causing more copper to leach into our water. We were told that after we moved in, the copper pipes would leach for a little while, and then stop. They never stopped. But, as soon as we turned off the water filter they did. We were getting blue marks in the shower and tub that just kept coming back until we turned off the filter. I really miss the way our shower water smelled and being able to drink from any faucet in the house, but I'd rather have to go use the filter on my fridge than to drink excess copper. I'm going to have to put end-source style filters on our shower heads though and where our bath water comes out (not sure how I'm gonna do this) for the chlorine though.
I think some people have PVC plumbing, but I'm not sure about that. I'm not sure what affect the water would have on those types pipes.