Its not particularly revolutionary to say “don’t conceptualize anything that might be really really hard to do.” or “don’t start with Photoshop” I suppose designing a website with an empty text editor is better. You may know you can do everything that you visualize, but most of the time you aren’t being revolutionary. Start with an idea, or a sheet of paper and a pencil.
Another thing that people should note: usability is a heavy word that people often push about. Granted, it must be usable, but it also must be attractive and rich enough so that people won’t pass it by. Usability is a component of good design, it is not an excuse to not design.
I’ve said it time and time again: usability and attractiveness are both subjective. What I find usable you may find unusable, and likewise what I find attractive you may find hideous.
However, there are some things which the majority of people agree on. Also, some things are dependent on your target audience, like Purposeless said in regard to Flash menus.
You have to find an equilibrium with the content-design-usability trinity. As long as the majority (or even better, all) of your users have no problems accessing your site and its content, then you’re good to go.
I favor drawing a mockup (pencil and paper, Photoshop, whatever) because it allows you to get an overall view of how your content, design, and usability will come together. And from that you can realize your vision.