So far, I have found 90%+ of the labels I've encountered come off easily with a 24-48 soak in tap water & dishsoap, the vast majority literally just fall off when removed from the water. The exceptions seem to be Ohio Brewing Co. bottles, and Duchutes bottles, both of which leave a SLIGHT glue residue. To remove this residue, the best/easiest thing I have found so far is a ChoreBoy copper scrub pad.
My process (so far, subject to refinement) is to put 12 bottles in a bucket or large pan, fill with hot tap water and dishsoap and cover. I then set the bucket in the dining room until my better half starts complaining about it being in the way (usually 24-48 hours), then I take the bottles to the sink and rinse them, easily removing any leftover glue residue from the mentioned bottles with the above mentioned ChoreBoy.
My method has worked to perfection so far (well over 100 bottles cleaned this way), but I may try an additive in the future if I encounter some really stubborn bottles.
SC