I don't think its looking dated at all and most people I know who aren't Mac users can't believe how amazing it looks. Maybe that's the problem, that those of us who use it on a daily basis have become very blase about its design. There's still nothing else out there that comes close to what the iMac achieves in its unique form.
Like I said, it might not look all that dated now, but fast forward 3 years and it will. The white acrylic will be something we'll look back at and laugh I think