My latest project was the conversion of a PSD file to a fully functional WordPress theme.
Features:
- Child theme based on the Hybrid framework
- Use of sIFR for the headings
- Use of CSS3 rgba for transparency, for IE, use of proprietary declarations in conditional stylesheet

How does siFR fare with SEO? I haven’t been able to find a conclusive discussion concerning it.
Actually, sIFR creates flash elements, so I don’t think it’s ideal as a font replacement solution.
I’d use Cufon if I had to do it again