Today I wrote this bit of code which I was quite pleased with:

input[type=submit]{display:none;}

This is targeting the sign up button on an email subscription form. Not every browser will understand this, so IE6 for example will just ignore it. For my purposes this is fine. My logic is that people on IE6 probably need the submit button anyway, whereas those who use more modern browsers which will understand this declaration will also be familiar with the fact that hitting enter will submit their form. An unusual approach to progressive enhancement maybe, but it made me happy…