-webkit-box-sizing
This site's search field has been virtually unusable in Chrome and Safari on Windows for several months. Fixing it was not high on my priority list, but I finally got to it this evening.

- Before
I did my best to get these browsers to respect the padding values that I'd assigned in my style sheet, getting aggressive in the Web Inspector. No joy.
I then noticed a curious property, -webkit-box-sizing. Sure enough, this was
the culprit. Safari and Chrome both use border-box as the default value,
which means that padding does not add to an element's dimensions the way it
does in the standard box model.
Specifying content-box fixed the problem.

- After
This is an extremely satisfying solution as it neatly targets the source of the problem.
The question remains as to why these browsers default to border-box as the
box-sizing for input elements with type="search". I don't know whether
default styles are specified at the rendering engine level or at the browser
level, but either way I would say that it's the result of Apple fiddling with
the controls to make search inputs look sexy on Mac OS X (where they're
rendered very differently).