I was very pleasantly surprised with my score. I had only started studying from late January, and only during odd hours before or after work so I really wasn't expecting to do so well. But I scored a 515 (129 Chem/Physical, 128 CARS, 128 Bio/Biochem, and 130 Psych/Soc) on the AAMC practice exam taken just a few days before the exam (that was the only practice exam that I had the chance to take.. that's how short I was on time). Then on the actual exam I even more surprisingly did very well and scored a 521 (131 Chem/Physical, 130 CARS, 129 Bio/Biochem, and 131 Psych/Soc).
Personally felt the practice exam was a little more difficult (more vague wordings in answer choices, etc.) than the real one.