That said, I have trouble believing that changing the buttons from labels to icons could have possibly tested as an improvement. I'm with the OP; I have to mouse over every button and read the tooltip to find the Report Spam one.
http://jasoncrawford.org/2012/04/how-to-cope-with-the-gmail-...
It shows how to: get rid of "importance" markers, add some contrast back to the colors, remove superfluous whitespace, and most importantly, change the impenetrable icons back to text.
I'm failing to come up with a link at the moment, but I remember a widely circulated bit of folklore about how an unnamed engineer within Google set up a cronjob that anonymously e-mailed the entire team a single number every day. After a while people figured out that the number was the byte count of the front page, the implication was that it was a metric that needed to be watched carefully.
http://blip.tv/oreilly-velocity-conference/velocity-09-maris...
Just watch from 1:00 to 2:00 -> One Minute will answer the question.
Here she tells the story, how the first Google Design came to live. It is quite interesting. It seems, that minimalism wasn't a rational choice and that it came to stay only, because the data proofed it to be the right lucky choice.
I can understand, that the minimalistic homepage was a point of pride. I would be proud, to minify the homepage of the company I work for.
As for the world's simplest homepage, that was the reason I switched from AltaVista to Google in the first place. I only started noticing the better search results after I switched to avoid the clutter.
They just realised that users came to google to perform a single, clearly defined task and decided the home page should reflect that.
I wouldn't argue it was "respect for minimalism" but it was respect for functional simplicity.
