This article comes off as hand-wavy. The crux of the argument, that "[t]op aligned labels have proven to be faster and easier to fill out than left or right aligned labels", is unsupported. The author supplies no links to research or other corroborating sources.
The graphic is a little misleading, too. Under "Top aligned labels", it says: "less vertical space". I initially understood that to mean that the form occupies less vertical space. It really means that the form leaves less vertical space below it.
I'm confused why they didn't consider other types of labels, especially for text boxes. For instance, the iPhone puts the labels inline with the form element. And placeholder text frequently replaces labels, anyway. How does that affect usage?
Interestingly, they don't follow their own advice. The comment form after the article uses right-aligned labels.