Gerrymandering is a political evil we are generally free from in New Zealand. Our electorate boundaries are set by an independent Representation Commission, which while it has party representatives on it, is constrained in the criteria it can use in deciding electorate boundaries, and seems to produce fair results. In addition to that, the advent of MMP means electorate boundaries matter a lot less anyway.
Things are rather different in the US. While it varies from state to state, the general rule is that boundaries are drawn by the politicians themselves, who shamelessly use their control of the process to stack the system in their favour. Traditionally, this has seen bipartisan gerrymanders, where incumbents collude across party lines to preserve their majorities and produce uncompetitive races. More recently, we've seen more overtly partisan gerrymanders, as parties (particularly Republicans) try and leverage their control of state legislatures into a permanent lock on power at a state or federal level. This behaviour is now so entrenched that in the US it can be fairly said that the voters don't choose their representatives - rather the representatives choose the voters!
If you want to see how this corruption works, there's a nice interactive example online: the redistricting game.