The biggest difference between the OASC and anything like PILAPT is that the RAF pretty much test you to destruction, it just keeps getting harder and harder. Eg 10digit numbers with 4secs to remember them, 3 puzzles happening all at once, orientation of aircraft, noises, spacial awareness, rudder and joystick controls. They also last for hours, i cant remember how many, but i seem to remember most of the morning and as heliskier said, its a 6am start!
The medical fact about aptitude testing is that you cannot learn it, you either have it or you dont and you dont get better at it by practising. Buying programs will not improve it either, but what they will help you to do is relax more which is quite valuable in these tests.
The Fighter Controller test is known as the hardest test at OASC, Navigators take a similar test (although i dont think they are called navigators anymore! showing my age....) if you pass that then you automatically pass for Pilot.
Also as slight hint, if you need to ask Heliskier what is involved in the day and you dont know the RAF inside out, eg how many weeks at IOT etc then get the books out now or down your RAF CO! Also know every aircraft in the RAF and where they are based and what their roles are, eg GR4 Vs F3. The idea of the interview used to be to press your knowledge until you cracked or if you obviously knew the subject they moved onto the next question.
Interview and Aptitude testing to be honest is the easiest bit. Its the exercises on the other days that are so easy to screw up and these can definitely be practised - make sure you know your speed distance time inside out and back to front!