I think Sephr is referring to the fact that many fonts look absolutely terrible on versions of Windows that don't have font smoothing enabled, namely XP. We almost threw out using custom fonts after we saw what our website looked like in XP.

I wrote up an article not too long ago about how we worked around this, which I feel weird mentioning because I just posted this on another thread like two days ago, but oh well:

http://dev.codio.com/graceful-degradation-for-non-web-standa...