@font-face is kind of confusing as all the browsers cannot decide on a single file format to use. Below is what I am currently using to add 1 new font to a site, you can see there is 4 separate font files, I know that each one is because some browsers support different formats but does the browser download all the files or just the 1 that it needs?
@font-face {
font-family: 'Oswald';
src: url('oswald-webfont.eot');
src: url('oswald-webfont.eot?#iefix') format('embedded-opentype'),
url('oswald-webfont.woff') format('woff'),
url('oswald-webfont.ttf') format('truetype'),
url('oswald-webfont.svg#OswaldRegular') format('svg');
font-weight: normal;
font-style: normal;
}