Just make sure you have the PSU switched off, do the paperclip trick (google it), plug in the PCIe connectors, then turn on the PSU switch.
People have killed their miners by simply plugging in the PCIe connectors from the crappy BFL PSU when it was already powered.
The chance of getting shocked is quite low.
When my BFL power supply crapped out, I cannibalized an old dell computer, took out one of the crappiest ATX PSUs I've ever seen.
To get it to start, I stuck the needle of a compass (the drawing instrument) on the green and touched the casing of the PSU.
It's been working without a problem ever since.