I'd like to know more about using ems in my styles. I know they are a unit of measurement, and I gather that they are good to use when you want pages to resize nicely in browsers. But I'd also like to know lots more, like... how big is an em? What are the advantages/disadvantages of using ems?

I also feel like I'm in the position of "you don't know what you don't know" about ems, so if you'd just like to go on about them in any other respect, I'm happy to read it