[cpburns2009]

> Yes, this would be an issue if overused, especially in paragraph lengths of text. However, inconsistent font sizes are worse.

I should have clarified this better. I dislike low contrast text because it makes it hard to read which is popular with the flat UI trends. Opacity isn't used so much from my experience, but light grey text on white is which has the same effect. I agree that inconsistent font sizes are bad too.

> Borders have their place, but white-space should be preferred as the most neutral and inobtrusive strategy.

In the example from the article I think the bordered version is much more concise and clearly delimits the search box and list. White-space seems to be used too carelessly in an attempt to avoid any clearly defined borders.

> The article says you don't need a background colour for every button, which is good advice.

You don't need to give every button a colorful background. But each button should have at least a border or background to distinguish it from standard text. The background can be just a boring grey like the classic Windows dialog buttons.