I didn't have to think about this answer whatsoever! For me I would absolutely jump in a puddle. I think if you're wrapped up and wearing the right attire, such as a pair of wellies it's great fun and you keep dry. I remember puddle jumping as a child but don't recall diving into any leaves!
What puts me off leaves is what could be lurking underneath! Creepy crawlies, rubbish or worse animal muck! So I guess that's the simple reason why I wouldn't choose to jump in to a leaf mountain. It wasn't a leaf pile but a friend sat down in long grass at primary school and ended up covered in dog muck! That memory really sticks in my mind!