I have a dual basin sink. One side gets filled with hot water and Oxi-Clean Versatile (the scent-free one). The bottles get soaked in that. After 10-15 minutes the labels usually slip right off. I use a blue scrubby to get off as much of the glue remnant as I can. Then I rinse them very well under hot water in the other basin of the sink.
After a while, you should have a decent stockpile. At this point, I only save bottles that can withstand high pressure (like Belgian's and weizens). I have plenty of supply around for my typical needs, and if I need a lot of bottles on short order, I'll just grab some at the local shop.