How much current can it carry? Superconductors tend to lose superconductivity in the presence of a large magnetic field, limiting the amount of current they can carry. I don't know if the high Tc superconductors are more susceptible than the regular ones, but it's something to keep in mind.
If they can take a really high magnetic field then that would be really cool for projects like the LHC. A large part of what makes that project dangerous, difficult, and expensive is the large number of He cooled superconducting magnets it needs. The danger comes in when you get a cosmic ray or something that increases the temperature of the magnet so that even a small part loses its superconductivity. When that happens, the non-superconducting part rapidly starts heating up the rest of the magnet in a process called "quenching." The results of a quench can be quite catastrophic.