Search engine optimization (SEO) Interview Preparation Guide

I'd pick the low-hanging fruit. Eliminate excess (graphics, multimedia), cut your prose in half, and optimize the rest. (you could install mod_gzip etc. in less than an hour also). The main thing is to make sure that your home page loads quickly.
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Yes, CSS has made it possible to transform table-based layouts into CSS-based layouts. Typically this reduces page size by 25 to 50%. The ratio of content to markup improves dramatically.

This is akin to asking what is the ROI for usability. Speed is a key component of usability. Small improvements in speed can take critical pages below typical attention thresholds, and dramatically lower bail-out rates and abandoned shopping carts. I talk about this in the book, but compression alone can save 30-50% in size and bandwidth costs. Webmasters who have employed compression and optimization typically save 30 to 50% off their bandwidth costs, and retain more customers, and have improved conversion rates.

Yes, I have read that. That is poorly supported elsewhere, I spend the first chapter showing why response times are important, summarizing key research into HCI and response times. However, there are factors that can affect how we perceive delays, like feedback and task complexity. Attainability is another interesting area of research, with users adjusting "subjective time bases" based on the pace of particular systems. If Domino's usually delivers in under 30 minutes, and then one day took an hour, you'd certainly notice it.
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As far as I'm concerned, no. But according to the response time research that I read, and mention briefly in the book, you can have response times that are too fast, and this increases errors. But on the web, that is unlikely to happen anytime soon.
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Many of the weblogs I view source have lots of embedded formatting, like font tags and complex CSS classes. Many weblogs are also by their very nature verbose :) I'd advocate using higher-level type selectors in CSS, contextual selectors, and to be brief in decks and point to longer stories for those who want to read more. Writing succinct headlines is also important.

In general, cut your prose as much as possible, especially on high-traffic pages. Users don't read as fast on the screen. On the web, users are information foraging, trying to maximize the value of their time. They flit about like hummingbirds, looking for nuggets that interest them. One study I read showed that on average, users spend about 1 second per page, and rarely stay more than 10 seconds. Once they find an article they want, they'll stay longer.
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Yes, this is also called coding motion out of loops, and is one of Bentley's 27 rules for code tuning. Also, using local variables is much faster. Many of these refactorings are covered in Chapter 10, "Optimizing JavaScript for Execution Speed."

I don't advocate making your entire HTML page into one single line. Some editors can choke on long lines, older versions of the Oracle info server can choke on long lines, and if you email your pages (as we do at webref), some email programs can flag a virus in longer lines. So I advocate a max of 255 character lines to be safe, or a max of 2000 character lines to avoid problems with Oracle. Also, removing whitespace can break some JavaScript code, and make your code hard to read. You can avoid these problems by keeping unoptimized versions for any edits, and punctuating your JavaScript statements with semicolons.
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Too many HTTP requests. This is due to the overuse of images and external files. We're also seeing a trend of too many external JavaScript and CSS files in the HEAD. This delays the display of your content as they must load first.

Yahoo.com has the most highly optimized home page I have seen. They use URL abbreviation to save nearly 30% off their home page HTML. View source to see what I mean. But even Yahoo has bloated up, they have nearly 300 links on their front page. WebReference.com of course :) I like most anything from Zeldman and company, very clean and CSS-based. Though there's always room for improvement.
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