If you're starting a new web project today, you look at what technologies the browsers you're targeting already support with unmodified syntax. (I'd argue that that development model's a poor fit for the web, but that's a different question.)
On Windows systems, the kerning is very odd in a lot of fonts since they moved to the new rendering engine a while back. The spacing following a capital T is usually way too tight, and in some fonts there are a few other examples as well. This can render pages completely illegible at typical body text sizes.
That is an artifact of ClearType subpixel positioning. Firefox 7 or 8 onwards (I don't remember which) turn subpixel positioning off for several commonly-used fonts, listed in gfx.font_rendering.cleartype_params.force_gdi_classic_for_families.
Also, take a Windows 7 computer with a few Adobe professional OpenType fonts installed locally -- probably some that come with Creative Suite would do -- and just try selecting those fonts using CSS in recent versions of Firefox.
I have a feeling you're choosing the font incorrectly. Note that with DirectWrite, any weight modifiers ("semibold", "black", "light") aren't part of the font name any more. Instead you need to specify weight using the font-weight property. So instead of saying Arial Black as you would normally, you need to say Arial with weight 900: http://www.neowin.net/forum/topic/971376-firefox-displays-my...
This is not a bug, though -- this is correct behaviour.
Most currently available web fonts also seem to look terrible (poorly hinted, terrible aliasing) on Windows XP in Firefox, but since they don't look great in other browsers either and they look better in Firefox on Windows 7, I'm inclined to point the finger more at Windows XP than Firefox in that case.
That's because most downloadable fonts aren't hinted for ClearType. DirectWrite with its subpixel positioning can cope much better with unhinted fonts.