Tanks who can't, shouldn't. It's one of the reasons I'm looking forward to Cataclysm with promises of skilled based play coming back to the scene.
There is a syndrome called tank envy. This was particularly prominent in the Burning Crusade. Gone were the days of 40 man raids and in was ushered a new era of 10 man entry level and 25 man advanced raids along with 5 man heroic dungeons. Tanks were the leaders, the tough guy. The ones who didn't die unless their team let them down. Guilds literally fell apart when their main tank left.