If you can answer the question "why did you go with a full width header and a fixed width body?", you're probably OK (unless that answer is something like "well, the theme I downloaded from themeforest was fixed width, but the client insisted I use their old header in the new design, so I just mashed it into the template...")

Like most "design errors", I think what the author of e article is ranting about is designs that aren't fully though out - if you've asked yourself the questions "fixed or full width, or both?", "what sized fonts should the forms have?", "how much of the site it going to be long enough to scroll, and do the scroll bars behaviour need to be considered in the design?", then you won't have made these errors, or at least will have good reasons why they are not "errors" but behaviours you chose.

It is simply astounding the number of web pages that have poor appearance because the 'designer' never tested them on a different size monitor, or with different size fonts.

Having the sidebar always on so as to avoid the bounce is not a usability thing. Usability would suggest that you leave the defaults the heck alone. In this case though, it is a pretty minor infraction.

Rather, it is an aesthetics thing. They've decided the default behaviour is 'ugly', and they've decided to override it to make it look better. In this case they've decided that prettiness trumps usability.

Its sister element with id "rightelement" is actually fixed width, but I don't see the issue there since the majority of its contents are image elements and not text.

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That said, I agree with you set a max-width for text only enclosures, and a min-width for enclosures that have image elements.