You can't back out in the last 24 hours if it takes a project under funding. Trust me, this isn't new and it's been debated in circles outside HN for a long while (I could list dozens of kicktrolled campaigns). The consensus is one of the reason Kickstarter is winning the crowdfunding game is it is possible to back out -- if they change that, they change the game. This gives consumers more freedom. But I think extra large amounts need new rules -- or just forbid them (as painful as that is).