Yes, the practice exams are designed to give you an idea of how you would do on the actual PCAT if you take them under the suggested time constraint. If you do poorly on them, then chances are you will not do well on the PCAT either. Make sure you use the practice exam to figure out what you need to improve on.
The math section is a major pain in the butt. If you talk to more people you'll find that many of them don't finish on time and end up bubbling in C for every question towards the end. I was one of them and ended up doing relatively well on that section, though it was my worst. Work as hard as you can to get the math concepts down but don't freak out if you can't finish the section on time. You're not alone!
The Kaplan tests are harder, I took them over the spring and compared to the pearson practice tests they're harder, but then again the Pearson practice tests were too easy as i looked at my score for this june pcat couldn't have been more disappointed. Those practice tests gave me a false sense of security now i gotta study for the August pcat...FML