I notice all of them , 100% of the time. Twitter has a fairly good one, but even that s very clunky. I'm not saying they are all slow, but they are clunky, jumpy and unpredictable, which in many ways is worse than a webpage like HN that is 100% consistent, but sometimes times out. Predictability for me is more important than pay-it-later responsiveness. E.g. when i press the Pay button i 'm OK with waiting 20 seconds for the payment to process. What's unacceptable is the button standing still, not doing anything until a few seconds later, at which time i ve pressed it 10 times.