I fill my sink with water-as hot as I can get it.I then add Dishwasher Detergent-powdered, liquid, or a tablet.(all varieties seem to work well)
This seems to soften the glue real fast, and if you let it set for about an hour, the labels slip right off in the water.
For really stubborn glue-I use WD-40 and a razor blade scraper.WD-40 will remove the toughest glue.(a trick I learned working in a hardware store)