I think I'm one of your 25%! My last 10 applications have been turned down. Rejected 2004-8 so got a five strikes place in 2009. Rejected 2010-4, but with the five strike scheme gone there's no knowing when I'll get a ballot place again.
In the past it's been assumed to be 20,000 places for 125,000 ballot applications, so that's about 1 in 6.
This time it might be different, as this will be the first year that the 5-strikes-and-you're-in system won't be operating. There are many on this forum, including myself, who had 5 strikes and are pretty peeved at missing out on a guaranteed place for 2015. But what will happen to the places freed up? If they put them into the main ballot allocation it could reduce the odds of getting in, maybe down to nearer 1 in 5. However, they could make a lot more money by increasing the number of Golden/Silver Bond charity places. I wonder what they'll do?