I'm talking about the Me! Me! Me! mentality, the I am the site designer and I know how to use and interpret the design and interaction elements of my site mindset. It is often harmless or a refreshing touch of visual personality branding, but just as often an impediment to visitors, or consumers, in the case of a business.
Changing content-to-background tints and contrasts over time to convey content aging, is a mostly harmless trait, as long as you are aware that you will not really manage to convey that relation by just doing. Any artist is familiar with that -- some may take note of your expression and even place it in the same semantic compartment as you do, but it will either go unnoticed past or end up differently interpreted by most of your audience.
Which is okay -- post time, for those interested, is actually stated in text too, and we can read it at our leisure. Some, who found a really old article of interest, where contrast is prohibitively low, might find it annoying, and occasionally perhaps even close the feedback loop, so Shaun might cap the restyling on the right side of readable (like many designers, he does not discount for his audience not having fine-tuned their display gamma value / contrast settings, the way he and his closer circle have). Or readjust their browser's stylesheet settings, or even find Shaun's own review-with-contrast link.
Breaking behaviour from plaintext or HTML markup in the visitor comment widget, is a more harmful trend that has gained traction in recent months, with Markdown, Textile, and a few other competing WikiML markup variants, popular in some audiences. Typical often-heard arguments for these are that they offer a trade-off between plaintext and complex markups such as HTML or XML, a middle ground providing rich markup without the penalty of a burdensome, difficult markup language such as HTML.
This is unfortunately faux reasoning.
The programming language Pike used to have a manual written in one of these markup flavours, aptly and insightfully named BMML, short for Black Magic Markup Language. On the web, all forms of markup except plaintext (which is what people write with pencils on paper) or HTML, the lingua franca of web markup, which many have invested time in learning to a level they need, and which we can also reasonably assume that browsers will gain increasing levels of support for, for instance via clipboard cut and paste from hypertext enabled tools.
Everything else is black magic markup languages, whether they be called so, or phpBB, Textile, Markdown, TeX, WikiML et cetera. While each and probably all of them can claim readability, they can't claim writability, because users are not hard-wired with their syntaxes and the WYSIWYG coupling is not there; they are expected to already know, or even worse, learn how to adjust to your preferred niche markup language. Why?
And before you knee-jerk that they can just go on writing their plaintext and ignore all about the markup language, can they really? If they want to give you a *hug*, will it come out as a hug? If they convey their moods (like smiles! :-) and flirtation ;-) with emotions, do they come out as moods (like smiles! :
And even if your user is a highly advanced one, aware of your using an alien markup format, wanting to actually convey his intended text, character for character, and even if you did provide a short summary of the markup rules and/or gave a link to its full documentation, what are the chances that page tells you how to quote a *, or -, or some other BMML cue? The chances of figuring out that within fifteen seconds? Is it * and -? Is it even possible in your BMML flavour of choice?
BMMLs force your audience to jump through the hoops you prefer to jump through yourself. To you (and a subset of your readership, or really commentorship), BMML may improve your speed of typing, or comfort of producing the markup you intend, but to others, it imposes learning a new markup language of very limited application (other sites that jumped the same markup band-wagon).
The today common time investment of having learned one pan-web markup format or using is rendered useless on sites that do not support it, and running your own markup adds a steep learning curve to be able to write properly, for all but your closer circle of friends.
BMMLs are excellent in contexts where you can opt in on them, such as browser extensions offering BMML to HTML conversion of text area contents or comment form content type toggles, offering multiple choice text format options -- as long as the choice is with the user, you are offering improved functionality. When not, it is first and foremost an impediment to using your site or service.