The nice folks at Box of Meat pointed me at an article about SHOUTING in ALL CAPITALS.
There’s something about text in all caps that turns people off. Using it in a social context is often seen as yelling. But using it in a design context is often seen as bad read ability. People use text in all caps thinking they are emphasizing their message. However, what they are actually doing is de-emphasizing their message.
What’s the purpose of writing text that users can barely read? It’s self-defeating. The caps lock key is a key that designer’s should rarely use.
That’s particularly important for us to remember as we still send quite a lot of plain text email, and that’s one of the last places where we don’t have font weight, style and colour to use for emphasis. Whether you’re writing advertising copy, customer support email boilerplates or internal email stay away from all-caps. Your readers will appreciate it.