<p>My question revolves around CSS Fixed Layout vs a Float Layout that extends to fill the width of the browser.</p>

<p>Right now the issue I'm running into is to have the masthead resize depending on the width of the page (something that I understand isn't possible given current browser implementation of <a href="http://www.w3.org/TR/2002/WD-css3-background-20020802/" rel="nofollow noreferrer">CSS3's <code>background-image: size;</code></a>).  At this point, I feel like I've reached an impasse all around:  Do I rework the site to use a fixed CSS layout, or do I keep the current layout and try to make the masthead image expand to fill most of the space provided?  Moreover, what are the pros and cons of moving to a fixed width layout, and the other (unseen) ramifications of using one layout over another?</p>

<p>The site in question will be given as a comment to this question -- I don't want to be seen as trying to increase traffic to it.</p>

<p>Edit: Any other thoughts?</p>

If you are trying to expand your background-image to the width of your page, it is better to use a fixed-sized layout as there is no cross-browser method to making a background-image expand to varying sizes that are dependent on the visitors resolution.
Fixed width layouts provide more flexibility for the designer, but not for the visitor. If you create a layout that is X pixels wide, then you are able to fine-tune your website pixel-by-pixel to your liking whereas "float" layouts (I call them liquid layouts) are based entirely on percent values and therefore differ from computer-to-computer. I find this difficult because you can test the layout on your screen and not know how it appears on someone else's, and (for ex.) a 20px margin has more of an effect on a 768px or 960px fixed-width layout than it does on a 1280px-liquid computer screen.
The major con, IMO, to a fixed-width layout is the fact that it looks too small on larger screens and too big on smaller screens. 768px used to be a fairly standard fixed-width layout, but now that is too small as the world moves away from 800x600. Now 960px is fairly standard, which is too big for 800x600 but still too small on 1280x1024.
It all depends on your audience and how your site fits together. Some layout can be made liquid and work perfectly fine, while others must be fixed (like the one you described).