[Ultimate_death]

Technically, you should also make sure you unplug ide/sata cables before the power cable to them to prevent it grounding through the wrong cables. This shouldn't be a problem with new drives but it's something to be aware of.

Also make sure your motherboard mounting pins are in the right place or you'll end up scratching the hell out of your motherboard.

Finally, bear in mind that if you plug any hard drives into different slots on your motherboard (sata 4 not sata 3 etc), you might get a boot error from dodgy boot orders. Changing the the slots your pci cards are in can cause some driver annoyance too sometimes, but it won't damage anything at least.