The @font-face spec doesn't mention a font standard, and Microsoft have already said they won't implement TTF or OTF because the font foundries don't like it.

The @font-face spec doesn't mention a font standard, and Microsoft have already said they won't implement TTF or OTF because the font foundries don't like it. It's possible that IE will implement the upcoming WOFF (Web Open Font Format) standard in IE9 but I wouldn't rely on it.