* { box-sizing: border-box } FTW « Paul Irish.
The universal selector got a bit of a bad reputation when people used it as a CSS reset. There are some performance concerns when using it, but Paul Irish makes a great suggestion here.
border-box is a good thing, just as long as you can break the habit you’ve likely formed in the years up until now. Personally, I’m on board with Paul’s recommendation and beginning with my next project I’m going to give it a shot to see how I like it.