LukeW's seminal book, "Web Form Design" has an entire chapter (19 pages!) about label placement. Some notes:
This paper is cited as discussing a major eBay form design, explaining their methodology: http://scholar.google.com/scholar?cluster=106605571117736457...
This article is cited as having done the eye-tracking research for label placement: http://www.uxmatters.com/mt/archives/2006/07/label-placement...
The chapter starts out with the note that "it depends" for your specific usage.
A summary of the results are available on his blog: http://www.lukew.com/ff/entry.asp?504
He also discusses using inline labels on his blog: http://www.lukew.com/ff/entry.asp?687
The sad thing is that many people accept what they read in blog posts that are widely retweeted. Critical thinking is such an important skill, I'm surprised how many people don't have it. ( http://en.wikipedia.org/wiki/Critical_thinking )
Critical thinking involves using your own mind to think about an idea without research. Not many people can do this. Ideas are presented all the time. You either agree or disagree. If you are curious for evidence, then you do the research yourself. But don't agree or disagree on the basis that no research is presented, or on the basis that lots of research is presented. Either way is not critical thinking.
Apologies, but these sorts of observations/criticisms are fairly common on HN (I remember someone saying "they don't follow their own advice" about the Stanford web credibility guidelines), and I have to say I consider them pointless. Observing hypocrisy and pseudo-hypocrisy is necessary if you're making a decision that depends heavily on someone's character, like electing a president, but it's almost always irrelevant when assessing the merit of what someone says.
People often have good reasons for not implementing their own advice, too. Maybe it was a higher priority for them to get the word out rather than make sure everything public they do complies with it first. Sometimes it's a cost-benefit problem: improving blog comment forms probably won't make much of a difference to their bottom line, but improving a new user sign-up form very well could. Comment forms are also fairly standard in what information they expect and in what order, so again, probably not a huge payoff. In Stanford's case, they already have the credibility that comes with being Stanford. Etc.
Again, this just has no relevance to the claims on offer. You can evaluate them for yourself without wondering what the author's motives are.
I have no idea if the site is as sketchy as people claim, because I've never even heard of it before. But even if it is, I still wouldn't think the comment form comes anywhere close to giving unambiguous information about the author's motives. There are so many highly plausible reasons for this that you'd have to be thoroughly unreasonable to assume that it's strong evidence for any particular reason.
Sometimes they are actually written well enough or are so misleading that you don't even notice these things. I went to this article looking for affirmation of my own opinion (I happen to agree with the headline) and thanks to confirmation bias did not notice the comment form, and might have even bookmarked it or sent it along. Thankfully someone saved me a future embarrassment by pointing out that it's worthless as evidence, which is a large part of why I read the HN comments...
However, this is completely irrelevant to the idea in the article and does not take any merit off of it whatsoever. If you cannot judge an idea for the idea itself, what chance do you have at learning anything from anything you read?
The 'placeholder' text is a new attribute of HTML5. It allows you to specify the 'inline text'. It's suppored in modern browsers.
Reference: http://diveintohtml5.org/forms.html
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.