DVDdoug:
It's reasonably safe if you do your work when it's not plugged-in and insulate everything. Worse case, you create a short and blow the circuit breaker in your house when you plug it in or turn it on.
In addition to this, do your testing with the device plugged into a surge protector that has a disconnect switch. This gives you a way to quickly shut off power to the device without having to grab and pull a plug.
Also get a non-contact voltage tester. Any hardware store should have them for under $10. You can use this to make sure that power is truly disconnected before you start touching things.