Here are some GBA blogs that provide good reading for you:
http://www.greenbuildingadvisor.com/...aters-come-age (with 92 comments)
http://www.greenbuildingadvisor.com/...rs-waste-money (with 107 comments)
http://www.greenbuildingadvisor.com/...-water-heaters (with 90 comments)
http://www.greenbuildingadvisor.com/...-cold-climates (only a year old, and 13 comments)
You can search there for other relevant blogs and Q&A for more reading than you have time to do.