I destroyed many labels trying various methods found on the internet before coming up with this technique. The polymer clay slicing blade is the trick.
Step 1: Add Water to Rinsed Bottle
Put water in the bottle - enough to protect your microwave, but not so much that the water spills when the bottle is on its side and not so much that the water gets into the neck of the bottle. If you want more water to protect the microwave, you can put some in a separate, covered container outside the bottle.
Step 2: Microwave for About 1.5 Minutes
In my 1200-watt oven that brings the bottle to about 200 degrees F according to my IR gun. I usually have the label that I want to preserve down. I thought label side down might be safer if the label had foil or metal embedded in the label, but I have not had trouble with the foil collar or metal in the labels (front or back) burning or sparking - as long as the collar/label was fully adhered to the bottle.
Step 3: Remove Bottle Carefully
Be careful when you remove the bottle from the oven. If you accidentally got water in the neck of the bottle, hot air in the body of the bottle can force the water out, potentially spraying you with hot water. It's also possible to superheat water in a microwave (http://www.snopes.com/science/microwave.asp).
I've been sprayed once with hot water that I'm pretty sure wasn't hot enough to have been superheated. I have the mouth of the bottle pointed away from me as I remove the bottle from the oven.
Step 4: Remove Label
I test-peel a corner of the back label to see if the front label is likely to come off easily. I find that labels either come off very easily or with significant difficulty - there doesn't seem to be an in-between. I have had near-100% success removing "difficult" labels with a tissue slicing blade normally used for cutting polymer clay (or slicing histologic sections in the pathology lab - be careful!). Angle the blade at about 45 degrees so that it doesn't cut or crease the label.
Step 5: Reheat Bottle If Necessary
If the bottle cools too much, it'll have to be reheated (I use 30-second increments) to soften the adhesive on "difficult" labels. Be sure parts of labels with metallic or foil printing are face-down and protected by the bottle during reheating. The only time I have ever had sparking or burning of metallic print in a label was when a partially removed label was curled up alongside the bottle rather than being under it.
Step 6: Goo Gone?
Goo Gone is a very effective adhesive solvent and used to be my fallback when other methods didn't work. But it contains petroleum distillates and required heavy saturation of resistant labels - which then had to be aired out. I have almost never had to use Goo Gone (and then only in tiny amounts) since I started using the polymer clay blade. I would still use Goo Gone to clean the bottle itself if I were using the bottle in a project.