Different manufacturers have different rules: the other year Citroen told me they kept back some spaces for folk to book on the day - if you are there anyway just go up and ask the least obvious ones
Ive been for the last two years, first year not a chance, second year stood in a line of people for about 45 mins to miss out by 2 people too many infront..... might try the early approach this year.
It's pretty nice to go up the hill at speed. I went up in a Ford last year - I missed out on the Mustang because people in front did a shuffle to screw me, but it was still nice to get a ride in a Focus ST.