I code all the way through HTML/CSS. I don't use Photoshop for web design (beyond scaling photos and stuff like that). My take on why I skip Photoshop and go straight to HTML/CSS when designing web UIs: http://37signals.com/svn/posts/1061-why-we-skip-photoshop

I think it's crucial that anyone who designs interfaces for the web understands how to design and code in HTML/CSS.