I’ve been a fan of box-sizing: border-box ever since reading Paul Irish’s article * { box-sizing: border-box } FTW
I use it on most projects, and find that it really speeds things up, and makes setting out grids much easier, especially when using Sass and Compass. In a few places, though, you need to be a bit careful.
It seems like later versions of jQuery play nicely with it, but as I’m mostly working on Drupal projects, I’m often stuck with an older version, which means that Google Maps popups and jScrollPane elements go awry.
Still, simple enough to override:
.view-locations .gmap div {
box-sizing: content-box;
}