Hmm
well this 'new' Google has been what's loaded on my Mac for at least the past fortnight, if not longer (maybe a month?).
I just presumed that it was one of those gradual roll-outs, because I've not seen it at work. I did a bit of searching when I first noticed it (thinking Google might have 'flipped a switch' and everyone was seeing it) and therefore was expecting some mention on the Web - but no one else seemed to have noticed/written about it then.
The new sidebar icons are quite good, very simple and the different colours help, but I'm not sure about the shade of yellow they've chosen for the letter 'o' - it looks most odd when the 'o's are displayed in 'Goooooooogle'.
I think i remember reading somewhere that Google do study peoples' reactions to the specific colours they choose for various interface elements on their sites, and tweak accordingly. Maybe there are even different versions of the new homepage in circulation on the Web, 'beta-testing' new colour-ways, designs etc.