There's something about being sore after a workout that makes people feel like they've done something really good for their bodies. I'm not exempt from this, either-- I kinda dig the feeling of a good post-workout soreness. And I'd be lying if I said I didn't get a little giggly when my clients tell me how sore they are after training with me. Contrary to popular belief, though, being sore has absolutely nothing to do with the quality of your workout.
Muscle soreness is caused by microtears in muscle that happen as a result of overload. It can also be caused by muscle spasm, or even overstretching. Most people, even conditioned athletes, will generaly get sore when they do a new exercise or activity, or when they significantly increase the intensity of their current routine. Some people rarely, if ever, get sore, no matter what they do. Others get sore fairly consistently over time. Every body is different, and how people adapt to their workouts will vary from individual to individual. As a general rule, however, most people see the intensity of their soreness reduce over time, and after training for a while may not get sore at all most of the time.
So how do you know if you're getting a good workout, if not by soreness? Well, you'll know based on how you feel during the workout (did you work up a good sweat? Are your muscles burning? Is your heart pounding? Did you train at the top of your own personal level?), and you'll know based on your results (Are you getting stronger/faster/leaner/better? Are you making progress towards your goals?). Because, quite frankly, I don't care how sore you get from your workouts-- if you're not progressing towards your goals, something needs to be changed.
So no, getting sore doesn't mean much, other than that your body is doing something it isn't used to doing. Set goals, train hard, train right, and judge your progress from there.
Questions? Comments? Feel free to post them below!