Somewhat surprisingly, it not only contains no DRM (which would have been a deal-breaker for open formats; Microsoft tried introducing an IE-only DRM-locked TrueType variant, but wasn't successful), but also contains all the data that a desktop font does, only slightly rejiggered to make it unusable in existing desktop systems. (I'll give them a week before someone writes a script that rips WOFF fonts to TrueType fonts.) This is surprising because the commercial font industry, producing something that's labour-intensive and skill-intensive but infinitely copiable, has until now jealously guarded its intellectual property, refusing to license its fonts for embedding in desktop formats. Instead, now they're keen to license them in slightly obfuscated versions, with the understanding that browsers enforce a same-origin linking policy unless there is additional license information. (I was thinking that, if the industry wasn't keen on letting its vector fonts out onto the web, it could have been possible to devise a resolution-limited font format, based on several sizes of bitmaps, with vector hints (i.e., "pixels 36-40 are a vertical stroke"), and generate all intermediate sizes using an interpolation algorithm. Such fonts would, of course, degrade if scaled above the maximum resolution in the file.) Another rationale could be that the market for web fonts could eclipse that for print fonts, and web font licensing would be easier to enforce (web sites, after all, are findable, and presumably unlicensed fonts would be easy enough to detect).
Licensing issues aside, WOFF promises to provide more than merely letting you put your favourite fonts on your web site. While Firefox 3.6 will have basic WOFF support, the next version of the specification promises to give more control, allowing web designers to fine-tune typographical parameters, selecting alternate forms including ligatures, different types of figures (lining and old-style, tabular and proportional), proper small caps, alternate figures (such as swash capitals) and such.