Apple's been moving towards the computer as the focus of a home entertainment center for the last few years now. Part of that is going for a consistent look, both in their applications and in their computers, and apparently in their phones and iPod products. It's pretty well known that photos and videos look better against black backdrops plus glossy screens. So towards that goal, the consumer-oriented computers have been designed with photos and video in mind.
There's a reason why photo applications have black backgrounds and why TV sets have black borders. It's because they enhance the picture that's on the screen with greater contrast. It's the same way with the iMac. White doesn't cut it because it detracts from the picture on the actual monitor.
I personally like the new design very much. I like hearing how this will be great for viewing photos and video because that's much of what I do. Color accuracy isn't a big deal for me because I'm colorblind anyway. But I do love the look of the screen on my glossy MacBook Pro compared to the previous MBP I owned with a matte screen (yawn). Yes, I deliberately chose glossy and went elsewhere when the first Apple Store I went to said they had only matte MBP's. I wish I could trade my matte 30" Cinema Display (attached to a Mac Pro) in for a glossy 30" Cinema Display.
There are only two things I don't like about the current design. While the chin is a bit smaller, they didn't really lower the height of the 24" version; rather they just left more space between the chin and the desk. The new 20" iMac I bought will end up in a confined space with only 1/2" to spare on the top. I wish that Apple had allowed the screen to be lowered on the 24" model so I could have gotten one of those to fit in that confined space. A 24" glossy model would have been gorgeous.
The second thing I don't like is the inability to easily access the hard drive so I could replace it when the current one gets cramped. With the nearly 40,000 RAW-sized photos I have plus video and a Boot Camp partition, a 250GB drive gets mighty cramped, requiring me to get a 500GB external drive to hold my Aperture library. With the new machine, I got the biggest drive I could, the 750GB drive for the 20" and had to pay extortionist prices for the upgrade. A 750GB drive can be had for $180, but I ended up giving back a 320GB drive and getting the 750GB one for a lot more than the drive alone would have cost me. I build my own Windows PC's and hack just about every piece of hardware I have (including drives on MBP's, two Apple TV's, and drives on Mac Minis), but the thought of cracking open an iMac without breaking it seemed too daunting.
For those who don't like the glossy display, why not just pop off the glass? It's a matte screen underneath it and the glass is apparently not sealed on that tightly. I think I read the glass was held on by 16 tiny magnets, though I'm not sure how the glass was made magnetic.