I read about this somewhere recently. The muscle soreness you feel is actually tiny micro-tears of your muscles - that's why it's good to get lots of protein into you after you exercise. It's also a good thing because when they heal, they heal much stronger
I tend to get sorer the second day before feeling 'normal' again.
Also, all the personal trainers and taekwondo coaches I've work with this past year recommend only light stretching before exercise (but warm your muscles up first) and to do your deep stretching after exercising. You risk more injury when you stretch if your muscles are cold.
Just keep moving! And don't be lazy...
SW: 74.3kg - 1/1/09
CW: 71.1kg - 3/5/09