I QT. Every fish I've gotten recently has had ich, so I'm really glad I do. I keep a little 5 gallon tank running at hyposalinity with a sponge filter and a heater.
I've also been keeping a coral QT tank, but my coral QT period keeps getting shorter and shorter. It's hard to keep water quality good enough for demanding corals in such a stripped down system. One other thing I've started doing is remounting new corals on clean frag plugs. The idea is that things like ich which can be transmitted on frags will be on the frag plug more than on the coral itself.