It's sometimes tempting to use case for emphasis: uppercase and lowercase are well within the repertoire of useful graphic design tools. Graphic designers know that uppercase is slower to read than lower case, but in isolated phrases that's unimportant. But on the web there's a penalty to using just upper- or lowercase: it's not as accessible. Writing in normal sentence case conveys information. Specifically, the semantics of the sentence - particularly abbreviations - depend on the use of case, as this photo shows:
CSS provides a way around this: the
text-transform property. This allows you to write your content in full-sentence case, and display it in full uppercase or lowercase as desired for stylistic reasons. For example, if your design calls for <h2> tags to be in uppercase, use
Of course, this allows you to simply remove the property if you change your site design; no content needs to be rewritten.
Some offenders even publish an RSS feed using uppercase titles. Never do this. People who want to syndicate your feed normally want it in sentence case, and there's no way to force that to happen if you aren't publishing the RSS feed using proper sentence case.