I don't when traveling since I think the additional bulk & weight just aren't worth it. Almost all notebook travel adapters can handle 110/240 VAC input so if you're using it in the US you already have a 100% safety margin. Yes spikes can be of 400V or more, but rarely occur over 1-2 cycles which is easily handled by the power supply. Also most switching supplies are designed to crowbar the output if the voltage goes too high. I haven't heard of anyone who's fried a laptop with the exception of a lightning event.

At home however everything's on a UPS, I'm retentive.