[Power Hungry]

ALWAYS... ALWAYS... ALWAYS... unhook the NEGATIVE battery cable first. There's not conflicting story on this, this is how it is and is basic Mechanics 101. There are two reasons for this:

1) If you are wrenching on the positive terminal and happen to bump the body or any other metal part of the vehicle or engine, you have an instant arc welder. Since nearly every car manufactured today is "negative ground", meaning that the the negative battery terminal is attached to the body, frame, and engine, if you were to accidentally short your wrench while undoing the negative cable, nothing will happen. If you short across the battery terminals... well, it wouldn't matter which side you are working at that point.

2) If you remove the positive battery cable and it should happen to touch the negative battery terminal or body, there is a chance that you could cause a sudden capacitive discharge in any of the onboard electronics which could damage them.

After removing the NEGATIVE battery cable, many people say to turn on the headlight switch in order to induce a drain to discharge any residual stored voltage in any of the electronics, including the PCM. Since in most cases there is already about 300-500 mA of current draw on the vehicle's systems, not to mention additional load from the dome lamps (if the doors are still open) and the hood lamp (if it's not broken), turning on the headlights won't hurt but probably isn't necessary. I've always let it sit 10-15 minutes, but seriously doubt anything over 30 seconds is necessary. Considering that the KAM (Keep Alive Memory) is akin to the memory presets of your radio, you'll find out in short order how long it takes to clear the PCM.

Hope this helps.