I've never done this, and I've built 100s of computers. However, I'm not standing on carpet or someplace that static could easily build up. I just always mount and plug in the power supply first. Once that's in the case, touch the case and you'll be grounded. You just have to keep grounded by using the case.3.) If you are handling expensive parts, you should wear a static wristband. I don't care what a computer store employee does, as from my experience from them they can't spot a power malfunction in a computer part if they tried, and if they ever do like hell are they going to take responsibility. They're not being safe not because it doesn't matter, it's because they don't care. I care. You should care.
I understand people wanting a static wristband though.