This is why I always immediately disable the trackpad clicks on laptops and netbooks. There's no tactile response, and due to the delay in Windows (it's as inevitable as the sun setting) I find myself opening a document 5 times whilst trying to figure out if I even double clicked it once.
I've used iPhones and Touches, yet to get hold of an iPad but this definitely hasn't been my response. It generally reacts fast enough to not need tactile response. Generally. I suppose when it goes wrong it's disastrously annoying for end-user experience.