For a photoshop-like web design tool, it would probably be a poor idea to have it output to HTML + CSS, as it would be insanely difficult to get remotely decent HTML + CSS (especially HTML + CSS that responds to interaction well). Even if you managed that, any decent front-end developer would probably rewrite it themselves to get the best interaction, "bulletproof-ness", and optimization possible. What would be far more useful is a design tool that incorporates HTML + CSS by using them for the layout of the image, but doesn't attempt to write them decently. Doing so would make it easy to use CSS to quickly change something like the font, while not trying to write decent front-end code.

In addition, I'd love it if this tool had the following. Even if it only had one of these things, I'd probably buy it.

1. Way to easily deal with text. In photoshop, text is a pain to deal with, especially for things like navigation. If there was a way to easily style the text of a file with css in addition to a gui method, things would be much more pleasurable and efficient.

2. Decent ways to include header, sidebar, and footer elements. Currently, a designer has to duplicate these across multiple files which makes updating even a snippet of text an arduous process involving opening many files.

3. A common browser element palette. Currently the only solution (That I know of), is to get a psd with the elements pre-made and try and fit whatever you get with into a design, which makes things like adding decent amounts of text to buttons rather bothersome.