He is one of the best keepers in the world but that doesn't mean he wont make mistakes. I thought he was partly culpable for both goals v Spurs, more so the 2nd, where he inadvertently turned a Spurs attack into a one-on-one situation. However, I also remember him in the same scenario multiple times in the home game v Arsenal, where he pulled off a couple of magnificent one-on-one saves.
HIs decision-making could certainly improve but his style of play is exactly what is being asked of him by the manager and it is a risk-reward style...sometimes he will take the risk and get it wrong.
I have no idea who people think we should be replacing him with, it would take a lot of money and a significant amount of luck to replace him with someone better.