I've actually never done a QT before. I have had beginner's luck with a lot of fish, for example my GBRs have survived all the crap I have put them through, everything from massive tank die-offs, to ick infections (introduced by neon tetras, unfortunately), and mini-cycles. It just happens for a reason.
I currently don't have the room for a QT tank, so it's not an option for me unfortunately...but I am trying to get one eventually after reading all the horror stories of what can go wrong when you don't QT.