Last year, I took the practice test in the PSAT Bulletin the night before. I timed myself and tried to take the practice test as if I was actually taking the real one. It meant that I didn't go to bed until about 1:00 in the morning, which probably wasn't the best thing to do. But I do think that the practice test helped me. It helped me become familiar with the test format so that there were no surprises during the real test, and I knew how to pace myself. I ended up scoring 9 points higher on the real test than the practice (your score's not guaranteed to go up on the real test, of course, but I think the chances of it increasing are greater than if you were to take the real test "cold"). Anyway, those +9 points meant that I qualified for Nat'l Merit Semifinalist, so I think the practice test is definitely worthwhile, if you have the time. If you don't have enough time, definitely seek out a mixture of sample PSAT questions, so that you're familiar with the type of questions that will be on the test.