I always start with sketching.  I usually start brainstorming on my whiteboard jotting down ideas, moods, emotions, colors, about what I want to convey and how.  Once I have a good list of things I start sketching.  Only once I have a solid foundation for the site on paper do I open up Photoshop.  From this point I usually crate a mood board with colors and inspiration that depict and compliment my design, and I start the mockup  process.

Starting on the computer will more than not leave you frustrated and drained.  It consumes time and energy creating mockups only to find by the time you are done you hate it.  Something that could have been determeined in half the time with paper and pencil.

Paper Before Pixels!!!!

Always sketch first. I find the computer can get in the way, and I can get stuck in a design rut if I move to the mac to early. Sketching helps keep the creativity flowing, and allows me to think up some organic ideas. I can decide what characteristics a typeface should have in a design without worrying about if I have it on the computer for example. Anything's possible on paper.

Sketching every time! Its easier for me to get my ideas together with a pencil and pad, then translate them onscreen.

It really depends on client needs. Every time a work need a bit more creativity sketching become necessary. In the rare cases where client know what he want's or already have a good idea of how the page elements should look like I run directly into html, css (without PSD), the use of css frameworks like blueprint and bluetrip made it a lot easier and overall faster than create the design in photoshop first.

It depends on my mood, the situation and the brief but usually I brainstorm a little bit to get some ideas down. Then I try to sketch out a few of these ideas, picking out the key elements or main or best ideas. After this then I move onto the computer. If I'm designing a website I'll move straight onto wireframing the site, then designing it. If it's a normal design, I'll just move straight into designing it as sketching should have given me a more solid idea of the layout, colours etc.

I agree stetch first.