Completed it only recently, 33 questions in 30 mins I think. I answered maybe 15 to 20 questions and only 70 percent of them were probably right. The first few and last few are easy but some of the middle questions are challenging unless you have been exposed to more complex tables and info, like economics or business for example.
The best prep I think would be the Qantas website and the practice questions given there. Fairly close to the mark. I think the main purpose is to drain the brain for the physcometric (spelling???) test you do straight afterwards.
I dont think it has a big bearing at all. As mentioned previously the sim and interview are the main things to focus on. I did get the early Chrisi present as well. 747 early next year.