Analogue boxes do breakdown. I had two before I switched to digital and I have had 4 digital boxes so far. But the digital picture IS far better than analogue, especially when projected on to an 83" screen. Then you can really tell the difference.
But an interesting point is that no one is manufacturing analogue boxes anymore, so NTL are using up there existing stock. At some point they will run out of them. And as a digital customer I will be dissapointed when they turn off the analogue as I get the 5 terrestrial channels through my digital box as analogue signals which I push around the house to 4 TVs. If they turn off the analogue then I have to get more digital boxes or reconnect the arial on the roof....if its still there...so I'm in no rush for NTL to turn off analogue !!