I don't like keeping the old labels on the glass jars I reuse so I thought I'd share some easy ways to remove them :) I use GT's Kombucha bottles for dressings, although they're a bit tough to clean, and coconut oil jars for a multitude of things. I've found these to be the easiest ways to remove labels:
A totally paper labels can be soaked in hot water (on the outside) and usually just peeled off. Put the jar in a taller bowl and fill the jar with hot water, letting it over flow into the bowl until the water reaches the top of the label. Let it soak for a bit (10ish mins) and go at it!
If it's a plastic-y label (like GT's), fill the inside of the bottle with steaming hot water for 5-10 minutes until you can touch the outside of the bottle for 10 seconds without it getting too warm on your fingers. Start peeling back the label - works like a charm to unstick the label!
Alas, if the outside of your jar has leftover sticky glue on it, grab some olive oil and rub it on with your fingers pressing hard enough to loosen up the glue. I'll usually do this for 5 mins, wash it off, and do it again later as well. This also works quite well :)
If anyone else has some good ways of removing labels please let us know!