Fonts loaded through the CSS3 @font-face mechanism look horrible on QtWebKit on Linux, see this page for an example:
It looks ok in QtWebKit on OSX.
I just noticed it looks equally bad in Firefox on Linux, so probably the issue is with a lower level library used by both QtWebkit and Firefox (freetype?).
(Either that, or both call it with bad parameters like e.g. disabling all hinting)
Indeed, it looks bad to me on Firefox and Chrome under Linux, too. This is not a WebKit bug.