I went to school...I definitely think it's overpriced, but worth it because the places I was interested gave me the benefit of the doubt w/o experience. I am a girl though so you never know. I didn't want to be a bar back so I wasn't found of that option. My school has "short courses," one of which was bartending, (only for those 21 and up). The theory is that you learn how to bartend for $60...in actuality a bartender "showed" us how he made drinks, and we drank them thus negating anything we learned that evening. :-D
Ideally work in a busy place. Tips are usually better and once you've been thrown into the fire a few times you figure it all out (unless you work at a martini bar in which case you'll need to memorize 30-60 new drinks). "When" I get into school I want to try to do it 2-3 times a month just to offset loans if possible.