Last night, our kitchen hot water tap started misbehaving and wouldn't turn off completely without really wrenching it. By morning, wrenching it didn't work, and we resorted to using the shut-off under the sink. After about three used of the shut-off to control the water, it stopped functioning... leaving us to control the shut-off on the hot water tank. Almost immediately, I noticed the hot-water valve on the tank would leak a bit in certain positions, and decided using the shut-offs I installed around our whole-house chlorine filter would be my best bet.
The plumbing representative at Home Depot was excellent. He put a copper pipe cutter in my hand (to remove the bad shut-off), a new shut-off that would basically crimp onto the copper pipe, and gave me a walk through on how to install it and what parts to not use (connecting it to the existing flex-hose). We then grabbed some teflon tape and picked out our new taps... which were made by the same company as our old ones and almost identical in style (I guess we really liked it).