I made it a point on an alt to tank all the low level instances I could and probably one of the worst ones was in fact deadmines. It really was a lost cause doing that one. Stockades was also a total mess but still controllable and rather fun at times with the priest yelling "wait for sunders!!!" and this warlock who kept sending his pet into the OPPOSITE side we were attacking (so his pet would die and it would train on us.. and he wouldn't stop doing it). Once you're VC the worst is basically behind you until BRD. I stopped doing instances at strathlome/sholomace however, when the death knights made PuGs completely unbearable, so I guess there's a point when you just can't take it anymore. But if that happens just take a break and do something else for a while.

But think of these as an exercise. You think once you get into the high level instances that you're not going to have these problems? Think again. In fact I'd say the lower level ones tend to be HARDER because you don't have all the tools available to you at level 80. There is a severe shortage of people who tank in lower level instances, so usually people are just happy to have one. It's good practice and a nice way to meet new people, just don't let it get to you when it goes bad. That's also a big part of tanking.