I mean, look at this page, it has almost no graphic elements http://www.quora.com/Joel-Lewenstein/Life-Without-Photoshop
The whole site is one color header and bunch of comments.
Good luck designing one of those cssmania.com like sites (when your client ask you to) without Photoshop.
I would like to hear how would you design this kind of site without PS?
Not speaking for anyone else, but my usual design process goes something like this:
1. Identify the structure, in pure information terms.
2. Get a basic idea of the layout, often using just a pencil and paper, or a quick mock-up tool like Balsamiq.
3. Implement the basic structure using HTML, typically as a set of divs nested in some reasonable way.
4. Implement the basic layout using CSS, just enough to position the divs in the right sort of places.
5. Add a bit of placeholder text/images and start styling the details as necessary.
The answer to your exact question, however, is "I wouldn't". I think the page you cited is horrible on just about every level, and if that's the kind of result you are looking for from using PS, you're welcome to it.
Are you also going to design your iPhone or iPad apps in objective-c?
It's easy to use code for structure and basic skinning but if you need details you are simply going to have to take it through some editor