Embedding fonts on the web is a big issue lately :). With the @font-face css rule you are able to use none-web-safe fonts on your site (.otf, .ttf on Safari and Firefox, .eot on IE).
But these are raw fonts your are sending out. WOFF is a font format optimized for the web. The raw font is compressed and has a xml wrapper. (read the spec)
This font format is a proposal by Tal Leming, Erik van Blokland and Jonathan Kew and is supported by the major font foundries and type designers.
Today Firefox is already supporting the WOFF format. It is ready for use in the next version (3.6). We are all hoping other browsers soon support it too.
So, as we believe this will be the next format for typography on the web, Typemytype endorses the WOFF specification, with default same-origin loading restrictions, as a Web font format, and expect to license fonts for Web use in this format.