When I was learning to fly, the instructor would quite regularly cover the flight instruments, and I'd have to fly circuits without knowing how fast I was going, or how high I was. While it is easy to estimate speed & climb from your attitude (nose above the horizon & lots of throttle usually means you're going up, nose above the horizon and no throttle you're slowing down, and will soon stall and descend (quickly too!)), I would hate to have to do that without outside visual references like the pilots of flight 447.
However, I would imagine that a blocked pitot tube would not disable the artificial horizon (and if it does, then why?). The pilots should have been able to keep the aircraft flying using a cruise throttle setting (already set) and the artificial horizon. Having said that, it is easy for me sitting here to say that, without multiple alarms going off in a rapidly deteriorating situation. It could be that flight 447 was a unique set of circumstances, and these guys were test pilots.