spinning classes will certainly get you into shape, providing you push yourself. like any stationary trainer, you will get a better workout (on average) per minute than on the road - especially when it comes to city riding. you can push yourself much harder when there's no coasting (none of that here anyway ), no lights, no traffic, etc.

if the instructor's no good, you very likely will not like the class. and there are certainly drawbacks - no wind in your hair, terrible music at loud volume, no actual 'speed', and no real excitement to speak of. but, like i said, if you push yourself, it's pretty much like riding a 45 minute time trial. i usually push myself right to the verge of hurling, and when the class is over, i'm spent. try to leave yourself enough gas to ride home on.

i took quite a few classes a few years ago before a cycling trip to the pyrenees, and it was great preparation. these days, i'm more likely to go ride outside, or ride the trainer at home.

and hey - if you're hetero, single, and male, you'll be in the happy minority.