Hardware keys (aka dongles) range from simple and easy to crack to impossible to crack. CodeMeter from Wibu-Systems (
www.wibu.us) has survived multiple public cracking contests--just last week another contest in China with a $15000 prize went without a winner. Since you have to buy the dongle it's not suitable for every problem but for high $ software you can't beat it.
Software anti-piracy systems typically either are relatively easy to crack (by patching OS dlls) or place significant burdens on the end-user. A difficult choice to make.