Stupendously easy. Tools needed: Jack, jack stands, lug wrench, ratchet with T45 Torx (or allen equivalent, I didn't have one on hand), 14mm socket, piston compressor (C-clamp works well) and needlenose pliers. Easy peasy.
Here's the parts (shoes not done because fuck shoes)
Ensure parking brake is on
Pop hood, remove brake fluid reservoir cap and wrap reservoir in cloth.
Break lug seals
Jack it up and lock it up with the stand
Remove wheel. NO PIC SORRY BUT remove that jesus clip on the front of the caliper, looks like it's holding the caliper in place but really it isn't
Look behind the disc. See that rubber tube? There's a plastic cap keeping you from the next step. Looks like this:
Remove it. Then take your T45 torx or allen head and unscrew the caliper pin behind it. Once unscrewed, use your needlenoses to gently pull the pin away from the caliper mount. There's another one of these on the bottom, use the same steps to remove. While you're there, pull the pins out, re-grease (thanks Crowmolly!) and slide back into reset position.
Safely pull caliper (and inboard pad) from the disc, and set it where the brake line is not pinched or stressed. Hang it if you need to. It sits nicely on the strut though.
Use your 14mm socket (and breaker if necessary) to remove the two caliper harness bolts from the back.
Once it's off, the rotor should pull off the hub nicely. If not, get out the Kroil and soak, the pound it off there with a hammer. Take your new rotor and give it a nice bath.
Install on the hub. Use your compressor tool or C-clamp to press the piston back into the caliper. I like to use the old outboard pad as a brace too. Out:
Install new inboard pad in the piston. Install caliper mount, outboard pad and caliper by reversing instructions above. Don't forget that stupid clip that you will no doubt bitch and moan about because it's such a pain in the ass.
Reinstall wheel and lug nuts, remove jack and jackstand, remove cloth from reservoir and reinstall reservoir cap. Fire it up, press the brake pedal a few times until you feel regular pressure again. Give it a test drive, increasing speed and brake pedal force until you're confident the repair has been done properly. Park it, have a beer. Tell the wife.
While this is written for a Ford Focus, most disc brakes are largely the same. You may have a centering pin, or a screw holding the disc to the hub, or any manner of other hardware, but this is a good primer and general step-by-step for most front disc setups. Remember to always look up torque specifications for your vehicle and make sure you follow them when installing new parts!